www-lib-markdown/js/markdown.js

class MDTokenType {
	static Text = new MDTokenType('Text');
	static Whitespace = new MDTokenType('Whitespace');

	static Underscore = new MDTokenType('Underscore');
	static Asterisk = new MDTokenType('Asterisk');
	static Slash = new MDTokenType('Slash');
	static Tilde = new MDTokenType('Tilde');
	static Bang = new MDTokenType('Bang');
	static Backtick = new MDTokenType('Backtick');

	static Label = new MDTokenType('Label'); // content=label
	static URL = new MDTokenType('URL'); // content=URL, extra=title
	static Email = new MDTokenType('Email'); // content=email address, extra=title
	static SimpleLink = new MDTokenType('SimpleLink'); // content=URL
	static SimpleEmail = new MDTokenType('SimpleEmail'); // content=email address
	static Footnote = new MDTokenType('Footnote'); // content=symbol
	static Modifier = new MDTokenType('Modifier'); // content

	static HTMLTag = new MDTokenType('HTMLTag'); // content=tag string, tag=MDHTMLTag

	static META_AnyNonWhitespace = new MDTokenType('METAAnyNonWhitespace');
	static META_OptionalWhitespace = new MDTokenType('METAOptionalWhitespace');

	/** @type {string} */
	name;

	/**
	 * @param {string} name
	 */
	constructor(name) {
		this.name = name;
	}

	toString() {
		return `${this.constructor.name}.${this.name}`;
	}

	equals(other) {
		return (other instanceof MDTokenType) && other.name == this.name;
	}
}

class MDToken {
	/**
	 * The original token string.
	 * @type {string}
	 */
	original;
	/** @type {MDTokenType} */
	type;
	/** @type {string|null} */
	content;
	/** @type {string|null} */
	extra;
	/** @type {MDHTMLTag|null} */
	tag;
	/** @type {MDTagModifier|null} */
	modifier;

	/**
	 * @param {string} original
	 * @param {MDTokenType} type
	 * @param {string|MDTagModifier|null} content
	 * @param {string|null} extra
	 * @param {MDHTMLTag|null} tag
	 */
	constructor(original, type, content=null, extra=null, tag=null) {
		this.original = original;
		this.type = type;
		if (content instanceof MDTagModifier) {
			this.content = null;
			this.modifier = content;
		} else {
			this.content = content;
			this.modifier = null;
		}
		this.extra = extra;
		this.tag = tag;
	}

	toString() {
		return `(${this.constructor.name} type=${this.type.toString()} content=${this.content})`;
	}

	/**
	 * Searches an array of MDToken for the given pattern of MDTokenTypes.
	 * If found, returns an object with the given keys.
	 * - `tokens: MDToken[]` - the subarray of `tokensToSearch` that match the pattern
	 * - `index: number` - index into `tokensToSearch` of first matching token
	 * 
	 * @param {MDToken[]|MDSpan[]} tokensToSearch
	 * @param {MDTokenType[]} pattern
	 * @param {number} startIndex
	 * @returns {object|null} match
	 */
	static findFirstTokens(tokensToSearch, pattern, startIndex=0) {
		var matched = [];
		for (var t = startIndex; t < tokensToSearch.length; t++) {
			var matchedAll = true;
			matched = [];
			var patternOffset = 0;
			for (var p = 0; p < pattern.length; p++) {
				var t0 = t + p + patternOffset;
				if (t0 >= tokensToSearch.length) return null;
				let token = tokensToSearch[t0];
				let elem = pattern[p];
				if (elem == MDTokenType.META_OptionalWhitespace) {
					if (token instanceof MDToken && token.type == MDTokenType.Whitespace) {
						matched.push(token);
					} else {
						patternOffset--;
					}
				} else if (elem == MDTokenType.META_AnyNonWhitespace) {
					if (token instanceof MDToken && token.type == MDTokenType.Whitespace) {
						matchedAll = false;
						break;
					}
					matched.push(token);
				} else {
					if (!(token instanceof MDToken) || token.type != elem) {
						matchedAll = false;
						break;
					}
					matched.push(token);
				}
			}
			if (matchedAll) {
				return {
					'tokens': matched,
					'index': t,
				};
			}
		}
		return null;
	}

	/**
	 * Searches an array of MDToken for a given starting pattern and ending
	 * pattern and returns match info about both and the tokens in between.
	 * 
	 * If `contentValidator` is specified, it will be called with the content
	 * tokens of a potential match. If the validator returns `true`, the result
	 * will be accepted and returned by this method. If the validator returns
	 * `false`, this method will keep looking for another matching pair. If no
	 * validator is given the first match will be returned regardless of content.
	 * 
	 * If a match is found, returns an object with the given keys:
	 * - `startTokens: MDToken[]` - tokens that matched `startPattern`
	 * - `contentTokens: MDToken[]` - tokens between the start and end pattern. May be an empty array.
	 * - `endTokens: MDToken[]` - tokens that matched `endPattern`
	 * - `startIndex: number` - index into `tokensToSearch` where `startPattern` begins
	 * - `contentIndex: number` - index into `tokensToSearch` of the first token that is between the start and end patterns
	 * - `endIndex: number` - index into `tokensToSearch` where `endPattern` begins
	 * - `totalLength: number` - total number of matched tokens
	 * 
	 * @param {MDToken[]} tokensToSearch - array of `MDToken` to search in
	 * @param {MDTokenType[]} startPattern - array of `MDTokenType` to find first
	 * @param {MDTokenType[]} endPattern - array of `MDTokenType` to find positioned after `startPattern`
	 * @param {function|null} contentValidator - optional validator function. If provided, will be passed an array of inner `MDToken`, and the function can return `true` to accept the contents or `false` to keep searching
	 * @param {number} startIndex - token index where searching should begin
	 * @returns {object|null} match object
	 */
	static findPairedTokens(tokensToSearch, startPattern, endPattern, contentValidator=null, startIndex=0) {
		for (var s = startIndex; s < tokensToSearch.length; s++) {
			var startMatch = this.findFirstTokens(tokensToSearch, startPattern, s);
			if (startMatch === null) return null;
			var endStart = startMatch.index + startMatch.tokens.length;
			while (endStart < tokensToSearch.length) {
				var endMatch = this.findFirstTokens(tokensToSearch, endPattern, endStart);
				if (endMatch === null) break;
				var contents = tokensToSearch.slice(startMatch.index + startMatch.tokens.length, endMatch.index);
				if (contents.length > 0 && (contentValidator === null || contentValidator(contents))) {
					return {
						'startTokens': startMatch.tokens,
						'contentTokens': contents,
						'endTokens': endMatch.tokens,
						'startIndex': startMatch.index,
						'contentIndex': startMatch.index + startMatch.tokens.length,
						'endIndex': endMatch.index,
						'totalLength': endMatch.index + endMatch.tokens.length - startMatch.index,
					};
				} else {
					// Contents rejected. Try next end match.
					endStart = endMatch.index + 1;
				}
			}
			// No end matches. Increment start match.
			s = startMatch.index;
		}
		return null;
	}

	equals(other) {
		if (!(other instanceof MDToken)) return false;
		if (other.original !== this.original) return false;
		if (!other.type.equals(this.type)) return false;
		if (other.content !== this.content) return false;
		if (other.extra !== this.extra) return false;
		if (!MDUtils.equal(other.tag, this.tag)) return false;
		if (!MDUtils.equals(other.modifier, this.modifier)) return false;
		return true
	}
}

class MDUtils {
	// Modified from https://urlregex.com/ to remove capture groups. Matches fully qualified URLs only.
	static baseURLRegex = /(?:(?:(?:[a-z]{3,9}:(?:\/\/)?)(?:[\-;:&=\+\$,\w]+@)?[a-z0-9\.\-]+|(?:www\.|[\-;:&=\+\$,\w]+@)[a-z0-9\.\-]+)(?:(?:\/[\+~%\/\.\w\-_]*)?\??(?:[\-\+=&;%@\.\w_]*)#?(?:[\.\!\/\\\w]*))?)/i;
	// Modified from https://emailregex.com/ to remove capture groups.
	static baseEmailRegex = /(?:(?:[^<>()\[\]\\.,;:\s@"]+(?:\.[^<>()\[\]\\.,;:\s@"]+)*)|(?:".+"))@(?:(?:\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(?:(?:[a-z\-0-9]+\.)+[a-z]{2,}))/i;

	/**
	 * Escapes special HTML characters.
	 *
	 * @param {string} str - string to escape
	 * @param {boolean} encodeNewlinesAsBreaks - whether to convert newline characters to `<br>` tags
	 * @returns {string} escaped HTML
	 */
	static escapeHTML(str, encodeNewlinesAsBreaks=false) {
		if (typeof str !== 'string') return '';
		var html = str.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;');
		if (encodeNewlinesAsBreaks) {
			html = html.replace(/\n/g, "<br>\n");
		}
		return html;
	}

	/**
	 * Encodes characters as HTML numeric entities to make it marginally more
	 * difficult for web scrapers to grab sensitive info.
	 *
	 * @param {string} text - text to escape
	 * @returns {string} escaped HTML
	 */
	static escapeObfuscated(text) {
		var html = '';
		for (var p = 0; p < text.length; p++) {
			const cp = text.codePointAt(p);
			html += `&#${cp};`;
		}
		return html;
	}

	/**
	 * Strips one or more leading indents from a line or lines of markdown. An
	 * indent is defined as 4 spaces or one tab. Incomplete indents (i.e. 1-3
	 * spaces) are treated like one indent level.
	 *
	 * @param {string|string[]} line - string or strings to strip
	 * @param {number} levels - how many indent levels to strip
	 * @returns {string|string[]} stripped lines
	 */
	static stripIndent(line, levels=1) {
		const regex = new RegExp(`^(?: {1,4}|\t){${levels}}`);
		return (line instanceof Array) ? line.map((l) => l.replace(regex, '')) : line.replace(regex, '');
	}

	/**
	 * Returns a copy of an array without any whitespace-only lines at the end.
	 *
	 * @param {String[]} lines - text lines
	 * @returns {String[]} - text lines without trailing blank lines
	 */
	static withoutTrailingBlankLines(lines) {
		var stripped = lines.slice();
		while (stripped.length > 0 && stripped[stripped.length - 1].trim().length == 0) {
			stripped.pop();
		}
		return stripped;
	}

	/**
	 * Tests if an array of lines contains at least one blank. A blank line
	 * can contain whitespace.
	 * 
	 * @param {String[]} lines
	 * @returns {boolean} whether `lines` contains any whitespace-only lines
	 */
	static containsBlankLine(lines) {
		for (const line of lines) {
			if (line.trim().length == 0) return true;
		}
		return false;
	}

	/**
	 * Counts the number of indent levels in a line of text. Partial indents
	 * (1 to 3 spaces) are counted as one indent level unless `fullIndentsOnly`
	 * is `true`.
	 *
	 * @param {string} line - line of markdown
	 * @param {boolean} fullIndentsOnly - whether to only count full indent levels (4 spaces or a tab)
	 * @returns {number} number of indent levels found
	 */
	static countIndents(line, fullIndentsOnly=false) {
		// normalize indents to tabs
		return line.replace(fullIndentsOnly
			? /(?: {4}|\t)/g
			: /(?: {1,4}|\t)/g,
			"\t")
			// remove content after indent
			.replace(/^(\t*)(.*?)$/, '$1')
			// count tabs
			.length;
	}

	/**
	 * Attempts to parse a label from the beginning of `line`. A label is of the
	 * form `[content]`. If found, returns an array with element 0 being the
	 * entire label and element 1 being the content of the label.
	 * 
	 * @param {string} line
	 * @returns {string[]|null} match groups or null if not found
	 */
	static tokenizeLabel(line) {
		if (!line.startsWith('[')) return null;
		var parenCount = 0;
		var bracketCount = 0;
		for (var p = 1; p < line.length; p++) {
			let ch = line.substring(p, p + 1);
			if (ch == '\\') {
				p++;
			} else if (ch == '(') {
				parenCount++;
			} else if (ch == ')') {
				parenCount--;
				if (parenCount < 0) return null;
			} else if (ch == '[') {
				bracketCount++;
			} else if (ch == ']') {
				if (bracketCount > 0) {
					bracketCount--;
				} else {
					return [ line.substring(0, p + 1), line.substring(1, p) ];
				}
			}
		}
		return null;
	}

	static #urlWithTitleRegex = /^\((\S+?)\s+"(.*?)"\)/i;  // 1=URL, 2=title
	static #urlRegex = /^\((\S+?)\)/i;  // 1=URL

	/**
	 * Attempts to parse a URL from the beginning of `line`. A URL is of the
	 * form `(url)` or `(url "title")`. If found, returns an array with element
	 * 0 being the entire URL token, 1 is the URL, 2 is the optional title.
	 * 
	 * @param {string} line
	 * @returns {string[]} token tuple
	 */
	static tokenizeURL(line) {
		var groups;
		if (groups = this.#urlWithTitleRegex.exec(line)) {
			if (this.tokenizeEmail(line)) return null; // make sure it's not better described as an email address
			return groups;
		}
		if (groups = this.#urlRegex.exec(line)) {
			if (this.tokenizeEmail(line)) return null;
			return [...groups, null];
		}
		return null;
	}

	static #emailWithTitleRegex = new RegExp("^\\(\\s*(" + MDUtils.baseEmailRegex.source + ")\\s+\"(.*?)\"\\s*\\)", "i");  // 1=email, 2=title
	static #emailRegex = new RegExp("^\\(\\s*(" + MDUtils.baseEmailRegex.source + ")\\s*\\)", "i");  // 1=email

	/**
	 * Attempts to parse an email address from the beginning of `line`. An
	 * email address is of the form `(user@example.com)` or `(user@example.com "link title")`.
	 * If found, returns an array with element 0 being the entire token, 1 is the
	 * email address, and 2 is the optional link title.
	 * 
	 * @param {string} line
	 * @returns {string[]} token tuple
	 */
	static tokenizeEmail(line) {
		var groups;
		if (groups = this.#emailWithTitleRegex.exec(line)) {
			return groups;
		}
		if (groups = this.#emailRegex.exec(line)) {
			return [...groups, null];
		}
		return null;
	}

	/**
	 * Describes the type of a variable for debugging.
	 *
	 * @param {any} value - value
	 * @returns {String} description of type
	 */
	static typename(value) {
		if (value === null) return 'null';
		if (value instanceof Object) {
			return value.constructor.name;
		}
		return typeof value;
	}

	static #equalArrays(a, b) {
		if (a === b) return true;
		if (!(a instanceof Array) || !(b instanceof Array)) return false;
		if (a == null || b == null) return false;
		if (a.length != b.length) return false;
		for (var i = 0; i < a.length; i++) {
			if (!this.equal(a[i], b[i])) return false;
		}
		return true;
	}

	static #equalObjects(a, b) {
		if (a === b) return true;
		if (!(a instanceof Object) || !(b instanceof Object)) return false;
		if (a == null || b == null) return false;
		if (a.equals !== undefined) {
			return a.equals(b);
		}
		for (const key of Object.keys(a)) {
			if (!this.equal(a[key], b[key])) return false;
		}
		for (const key of Object.keys(b)) {
			if (!this.equal(a[key], b[key])) return false;
		}
		return true;
	}

	/**
	 * Tests for equality on lots of different kinds of values including objects
	 * and arrays. Will use `.equals` on objects that implement it.
	 * 
	 * @param {any} a
	 * @param {any} b
	 * @returns {boolean}
	 */
	static equal(a, b, floatDifferencePercent=0.0) {
		if (a instanceof Array && b instanceof Array) {
			return this.#equalArrays(a, b);
		}
		if (a instanceof Object && b instanceof Object) {
			return this.#equalObjects(a, b);
		}
		if (typeof a == 'number' && typeof b == 'number') {
			if (a === b) return true;
			const delta = b - a;
			const ratio = delta / a;
			return Math.abs(ratio) <= floatDifferencePercent;
		}
		return a == b;
	}
}


// -- Block readers ---------------------------------------------------------


/**
 * Base class for reading from an array of markdown lines and finding a block
 * of a given type. Readers are checked in `priority` order and `readBlock` is
 * called to see the reader implementation recognizes a particular kind of block
 * at the given line pointer, returning that block if so or null if not.
 * 
 * Inline markdown is processed in a separate stage by `MDInlineReader`.
 */
class MDBlockReader {
	/** @type {number} */
	#priority;

	/**
	 * A unitless relative priority value that determines which readers are
	 * tried first. Lower values are tried first. In the range of 0.0 to 100.0.
	 * @type {number} priority
	 */
	get priority() { return this.#priority; }

	/**
	 * Creates a block reader.
	 * 
	 * When overriding the constructor, it is suggested to allow the caller to
	 * specify an optional custom priority value, falling back to a reasonable
	 * default if not specified.
	 * 
	 * @param {number} priority
	 */
	constructor(priority) {
		this.#priority = priority;
	}

	/**
	 * Attempts to read a block of this type from the given read state. If
	 * successful, the state's line pointer should be incremented to the line
	 * just after the last line of the block and the read block should be
	 * returned.
	 *
	 * @param {MDState} state - read state
	 * @returns {MDBlock|null} the read block
	 */
	readBlock(state) {
		throw Error(`Abstract readBlock must be overridden in ${this.constructor.name}`);
	}

	/**
	 * Called after the full document has been generated for optional
	 * post-processing.
	 *
	 * @param {MDState} state
	 * @param {MDBlock[]} blocks - top-level document block list
	 */
	postProcess(state, blocks) {
		// no op
	}
}

/**
 * Reads markdown blocks for headers denoted with the underline syntax.
 * 
 * Example:
 * 
 * > ```markdown
 * > Header 1
 * > ========
 * > ```
 */
class MDUnderlinedHeaderBlockReader extends MDBlockReader {
	constructor(priority=0.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 */
	readBlock(state) {
		var p = state.p;
		if (!state.hasLines(2)) return null;
		var modifier;
		let contentLine = state.lines[p++].trim();
		[contentLine, modifier] = MDTagModifier.fromLine(contentLine);
		let underLine = state.lines[p++].trim();
		if (contentLine == '') return null;
		if (/^=+$/.exec(underLine)) {
			state.p = p;
			let block = new MDHeaderBlock(1, state.inlineMarkdownToSpan(contentLine));
			if (modifier) modifier.applyTo(block);
			return block;
		}
		if (/^\-+$/.exec(underLine)) {
			state.p = p;
			let block = new MDHeaderBlock(2, state.inlineMarkdownToSpan(contentLine));
			if (modifier) modifier.applyTo(block);
			return block;
		}
		return null;
	}
}

/**
 * Reads markdown blocks for headers denoted with hash marks. Header levels 1 to
 * 6 are supported.
 * 
 * Examples:
 * 
 * > ```markdown
 * > # Header 1
 * >
 * > ## Header 2
 * >
 * > # Enclosing Hashes Are Optional #
 * >
 * > ## Trailing Hashes Don't Have to Match in Number ####
 * > ```
 */
class MDHashHeaderBlockReader extends MDBlockReader {
	static #hashHeaderRegex = /^(#{1,6})\s*([^#].*?)\s*\#*\s*$/;  // 1=hashes, 2=content

	constructor(priority=5.0) {
		super(priority);
	}

	readBlock(state) {
		var p = state.p;
		let line = state.lines[p++];
		var modifier;
		[line, modifier] = MDTagModifier.fromLine(line);
		var groups = MDHashHeaderBlockReader.#hashHeaderRegex.exec(line);
		if (groups === null) return null;
		state.p = p;
		const level = groups[1].length;
		const content = groups[2];
		let block = new MDHeaderBlock(level, new MDInlineBlock(state.inlineMarkdownToSpan(content)));
		if (modifier) modifier.applyTo(block);
		return block;
	}
}

/**
 * Reads markdown blocks for blockquoted text.
 * 
 * Example:
 * 
 * > ```markdown
 * > > Blockquoted text
 * > ```
 */
class MDBlockQuoteBlockReader extends MDBlockReader {
	constructor(priority=10.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 */
	readBlock(state) {
		var blockquoteLines = [];
		var p = state.p;
		while (p < state.lines.length) {
			let line = state.lines[p++];
			if (line.startsWith(">")) {
				blockquoteLines.push(line);
			} else {
				break;
			}
		}
		if (blockquoteLines.length > 0) {
			let contentLines = blockquoteLines.map(function(line) {
				return line.substring(1).replace(/^ {0,3}\t?/, '');
			});
			let substate = state.copy(contentLines);
			let quotedBlocks = substate.readBlocks();
			state.p = p;
			return new MDBlockquoteBlock(quotedBlocks);
		}
		return null;
	}
}

/**
 * Abstract base class for ordered and unordered lists.
 */
class MDBaseListBlockReader extends MDBlockReader {
	constructor(priority) {
		super(priority);
	}

	#readItemLines(state, firstLineStartPos) {
		var p = state.p;
		var lines = [];
		var seenBlankLine = false;
		var stripTrailingBlankLines = true;
		while (state.hasLines(1, p)) {
			const isFirstLine = p == state.p;
			var line = state.lines[p++];
			if (isFirstLine) {
				line = line.substring(firstLineStartPos);
			}
			if (/^(?:\*|\+|\-|\d+\.)\s+/.exec(line)) {
				// Found next list item
				stripTrailingBlankLines = false; // because this signals extra spacing intended
				break;
			}
			const isBlankLine = line.trim().length == 0;
			const isIndented = /^\s+\S/.exec(line) !== null;
			if (isBlankLine) {
				seenBlankLine = true;
			} else if (!isIndented && seenBlankLine) {
				// Post-list content
				break;
			}
			lines.push(line);
		}
		lines = MDUtils.withoutTrailingBlankLines(lines);
		return MDUtils.stripIndent(lines);
	}

	/**
	 * @param {MDState} state
	 * @param {number} firstLineStart
	 * @return {MDBlock}
	 */
	readListItemContent(state, firstLineStartPos) {
		const itemLines = this.#readItemLines(state, firstLineStartPos);
		state.p += Math.max(itemLines.length, 1);

		if (itemLines.length == 1) {
			return new MDInlineBlock(state.inlineMarkdownToSpans(itemLines[0]));
		}

		const hasBlankLines = itemLines.filter((line) => line.trim().length == 0).length > 0;
		if (hasBlankLines) {
			const substate = state.copy(itemLines);
			const blocks = substate.readBlocks();
			return (blocks.length == 1) ? blocks[0] : new MDMultiBlock(blocks);
		}

		// Multiline content with no blank lines. Search for new block
		// boundaries without the benefit of a blank line to demarcate it.
		for (var p = 1; p < itemLines.length; p++) {
			const line = itemLines[p];
			if (/^(?:\*|\-|\+|\d+\.)\s+/.exec(line)) {
				// Nested list found
				const firstBlock = new MDInlineBlock(state.inlineMarkdownToSpans(itemLines.slice(0, p).join("\n")));
				const substate = state.copy(itemLines.slice(p));
				const blocks = substate.readBlocks();
				return new MDMultiBlock([ firstBlock, ...blocks ]);
			}
		}

		// Ok, give up and just do a standard block read
		{
			const substate = state.copy(itemLines);
			const blocks = substate.readBlocks();
			return (blocks.length == 1) ? blocks[0] : new MDMultiBlock(blocks);
		}
	}

	readBlock(state) {
		throw new Error(`Abstract readBlock must be overridden in ${this.constructor.name}`);
	}
}

/**
 * Block reader for unordered (bulleted) lists.
 * 
 * Example:
 * 
 * > ```markdown
 * > * First item
 * > * Second item
 * > * Third item
 * > ```
 */
class MDUnorderedListBlockReader extends MDBaseListBlockReader {
	static #unorderedListRegex = /^([\*\+\-]\s+)(.*)$/;  // 1=bullet, 2=content

	constructor(priority=15.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 * @returns {MDListItemBlock|null}
	 */
	#readUnorderedListItem(state) {
		var p = state.p;
		let line = state.lines[p];
		let groups = MDUnorderedListBlockReader.#unorderedListRegex.exec(line);
		if (groups === null) return null;
		const firstLineOffset = groups[1].length;
		return new MDListItemBlock(this.readListItemContent(state, firstLineOffset));
	}

	readBlock(state) {
		var items = [];
		var item = null;
		do {
			item = this.#readUnorderedListItem(state);
			if (item) items.push(item);
		} while (item);
		if (items.length == 0) return null;
		return new MDUnorderedListBlock(items);
	}
}

/**
 * Block reader for ordered (numbered) lists. The number of the first item is
 * used to begin counting. The subsequent items increase by 1, regardless of
 * their value.
 * 
 * Example:
 * 
 * > ```markdown
 * > 1. First
 * > 2. Second
 * > 3. Third
 * > ```
 */
class MDOrderedListBlockReader extends MDBaseListBlockReader {
	static #orderedListRegex = /^(\d+)(\.\s+)(.*)$/;  // 1=number, 2=dot, 3=content

	constructor(priority=16.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 * @returns {MDListItemBlock|null}
	 */
	#readOrderedListItem(state) {
		var p = state.p;
		let line = state.lines[p];
		let groups = MDOrderedListBlockReader.#orderedListRegex.exec(line);
		if (groups === null) return null;
		const ordinal = parseInt(groups[1]);
		const firstLineOffset = groups[1].length + groups[2].length;
		return new MDListItemBlock(this.readListItemContent(state, firstLineOffset), ordinal);
	}

	readBlock(state) {
		var items = [];
		var item = null;
		do {
			item = this.#readOrderedListItem(state);
			if (item) items.push(item);
		} while (item);
		if (items.length == 0) return null;
		return new MDOrderedListBlock(items, items[0].ordinal);
	}
}

/**
 * Block reader for code blocks denoted by pairs of triple tickmarks.
 * 
 * Example:
 * 
 * > ```markdown
 * > \`\`\`
 * > function formattedAsCode() {
 * > }
 * > \`\`\`
 * > ```
 */
class MDFencedCodeBlockReader extends MDBlockReader {
	constructor(priority=20.0) {
		super(priority);
	}

	readBlock(state) {
		if (!state.hasLines(2)) return null;
		var p = state.p;
		let openFenceLine = state.lines[p++];
		var modifier;
		[openFenceLine, modifier] = MDTagModifier.fromLine(openFenceLine);
		if (openFenceLine.trim() != '```') return null;
		var codeLines = [];
		while (state.hasLines(1, p)) {
			let line = state.lines[p++];
			if (line.trim() == '```') {
				state.p = p;
				let block = new MDCodeBlock(codeLines.join("\n"));
				if (modifier) modifier.applyTo(block);
				return block;
			}
			codeLines.push(line);
		}
		return null;
	}
}

/**
 * Block reader for code blocks denoted by indenting text.
 * 
 * Example (indent spaces rendered visibly for clarity):
 * 
 * > ```markdown
 * > ⎵⎵⎵⎵function formattedAsCode() {
 * > ⎵⎵⎵⎵}
 * > ```
 */
class MDIndentedCodeBlockReader extends MDBlockReader {
	constructor(priority=21.0) {
		super(priority);
	}

	readBlock(state) {
		var p = state.p;
		var codeLines = [];
		while (state.hasLines(1, p)) {
			let line = state.lines[p++];
			if (MDUtils.countIndents(line, true) < 1) {
				p--;
				break;
			}
			codeLines.push(MDUtils.stripIndent(line));
		}
		if (codeLines.length == 0) return null;
		state.p = p;
		return new MDCodeBlock(codeLines.join("\n"));
	}
}

/**
 * Block reader for horizontal rules. Composed of three or more hypens or
 * asterisks on a line by themselves, with or without intermediate whitespace.
 * 
 * Examples:
 * 
 * > ```markdown
 * > ---
 * >
 * > - - -
 * > 
 * > * * * * *
 * >
 * > ****
 * > ```
 */
class MDHorizontalRuleBlockReader extends MDBlockReader {
	static #horizontalRuleRegex = /^\s*(?:\-(?:\s*\-){2,}|\*(?:\s*\*){2,})\s*$/;

	constructor(priority=25.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 * @returns {MDBlock|null}
	 */
	readBlock(state) {
		var p = state.p;
		let line = state.lines[p++];
		var modifier;
		[line, modifier] = MDTagModifier.fromLine(line);
		if (MDHorizontalRuleBlockReader.#horizontalRuleRegex.exec(line)) {
			state.p = p;
			let block = new MDHorizontalRuleBlock();
			if (modifier) modifier.applyTo(block);
			return block;
		}
		return null;
	}
}

/**
 * Block reader for tables.
 * 
 * Examples:
 * 
 * > ```markdown
 * > Name | Age
 * > --- | ---
 * > Joe | 34
 * > Alice | 25
 * >
 * > | Leading | And Trailing |
 * > | - | - |
 * > | Required | for single column tables |
 * >
 * > | Left aligned column | Center aligned | Right aligned |
 * > | :-- | :--: | --: |
 * > | Joe | x | 34 |
 * > ```
 */
class MDTableBlockReader extends MDBlockReader {
	constructor(priority=30.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 * @param {boolean} isHeader
	 * @return {MDTableRowBlock|null}
	 */
	#readTableRow(state, isHeader) {
		if (!state.hasLines(1)) return null;
		var p = state.p;
		let line = MDTagModifier.strip(state.lines[p++].trim());
		if (/.*\|.*/.exec(line) === null) return null;
		if (line.startsWith('|')) line = line.substring(1);
		if (line.endsWith('|')) line = line.substring(0, line.length - 1);
		let cellTokens = line.split('|');
		let cells = cellTokens.map(function(token) {
			let content = state.inlineMarkdownToSpan(token.trim());
			return isHeader ? new MDTableHeaderCellBlock(content) : new MDTableCellBlock(content);
		});
		state.p = p;
		return new MDTableRowBlock(cells);
	}

	/**
	 * @param {string} line
	 * @returns {string[]}
	 */
	#parseColumnAlignments(line) {
		line = line.trim();
		if (line.startsWith('|')) line = line.substring(1);
		if (line.endsWith('|')) line = line.substring(0, line.length - 1);
		return line.split(/\s*\|\s*/).map(function(token) {
			if (token.startsWith(':')) {
				if (token.endsWith(':')) {
					return MDTableCellBlock.AlignCenter;
				}
				return MDTableCellBlock.AlignLeft;
			} else if (token.endsWith(':')) {
				return MDTableCellBlock.AlignRight;
			}
			return null;
		});
	}

	static #tableDividerRegex = /^\s*[|]?\s*(?:[:]?-+[:]?)(?:\s*\|\s*[:]?-+[:]?)*\s*[|]?\s*$/;

	readBlock(state) {
		if (!state.hasLines(2)) return null;
		let startP = state.p;
		let firstLine = state.lines[startP];
		var modifier = MDTagModifier.fromLine(firstLine)[1];
		let headerRow = this.#readTableRow(state, true);
		if (headerRow === null) {
			state.p = startP;
			return null;
		}
		let dividerLine = state.lines[state.p++];
		let dividerGroups = MDTableBlockReader.#tableDividerRegex.exec(dividerLine);
		if (dividerGroups === null) {
			state.p = startP;
			return null;
		}
		let columnAlignments = this.#parseColumnAlignments(dividerLine);
		headerRow.applyAlignments(columnAlignments);
		var bodyRows = [];
		while (state.hasLines(1)) {
			let row = this.#readTableRow(state, false);
			if (row === null) break;
			row.applyAlignments(columnAlignments);
			bodyRows.push(row);
		}
		let table = new MDTableBlock(headerRow, bodyRows);
		if (modifier) modifier.applyTo(table);
		return table;
	}
}

/**
 * Block reader for definition lists. Definitions go directly under terms starting
 * with a colon.
 * 
 * Example:
 * 
 * > ```markdown
 * > markdown
 * > : a language for generating HTML from simplified syntax
 * > parser
 * > : code that converts human-readable code into machine language
 * > ```
 */
class MDDefinitionListBlockReader extends MDBlockReader {
	constructor(priority=35.0) {
		super(priority);
	}

	readBlock(state) {
		var p = state.p;
		var groups;
		var termCount = 0;
		var definitionCount = 0;
		var defLines = [];
		while (state.hasLines(1, p)) {
			let line = state.lines[p++];
			if (line.trim().length == 0) {
				break;
			}
			if (/^\s+/.exec(line)) {
				if (defLines.length == 0) return null;
				defLines[defLines.length - 1] += "\n" + line;
			} else if (/^:\s+/.exec(line)) {
				defLines.push(line);
				definitionCount++;
			} else {
				defLines.push(line);
				termCount++;
			}
		}
		if (termCount == 0 || definitionCount == 0) return null;
		let blocks = defLines.map(function(line) {
			if (groups = /^:\s+(.*?)$/s.exec(line)) {
				return new MDDefinitionDefinitionBlock(state.inlineMarkdownToSpans(groups[1]));
			} else {
				return new MDDefinitionTermBlock(state.inlineMarkdownToSpans(line));
			}
		});
		state.p = p;
		return new MDDefinitionListBlock(blocks);
	}
}

/**
 * Block reader for defining footnote contents. Footnotes can be defined anywhere
 * in the document but will always be rendered at the end of a page or end of
 * the document.
 * 
 * Examples:
 * 
 * > ```markdown
 * > [^1]: Content of a footnote. Anywhere `[^1]` appears in the
 * >   main text, it will hyperlink to this content at the bottom
 * >   of the document. There will also be backlinks at the end
 * >   of this footnote to all references to it.
 * > ```
 */
class MDFootnoteDefinitionBlockReader extends MDBlockReader {
	constructor(priority=40.0) {
		super(priority);
	}

	/**
	 * @param {MDState} state
	 */
	readBlock(state) {
		var p = state.p;
		let groups = /^\s*\[\^\s*([^\]]+)\s*\]:\s+(.*)\s*$/.exec(state.lines[p++]);
		if (groups === null) return null;
		let symbol = groups[1];
		let def = groups[2];
		while (state.hasLines(1, p)) {
			let line = state.lines[p++];
			if (/^\s+/.exec(line)) {
				def += "\n" + line;
			} else {
				p--;
				break;
			}
		}
		state.p = p;
		let content = state.inlineMarkdownToSpan(def);
		state.defineFootnote(symbol, content);
		state.p = p;
		return new MDMultiBlock([]);
	}
}

/**
 * Block reader for abbreviation definitions. Anywhere the abbreviation appears
 * in the text will have its definition available when hovering over it.
 * Definitions can appear anywhere in the document. Their content should only
 * contain simple text, not markdown.
 * 
 * Example:
 * 
 * > ```markdown
 * > *[HTML]: Hyper Text Markup Language
 * > ```
 */
class MDAbbreviationDefinitionBlockReader extends MDBlockReader {
	constructor(priority=45.0) {
		super(priority);
	}

	readBlock(state) {
		var p = state.p;
		let line = state.lines[p++];
		let groups = /^\s*\*\[([^\]]+?)\]:\s+(.*?)\s*$/.exec(line);
		if (groups === null) return null;
		let abbrev = groups[1];
		let def = groups[2];
		state.defineAbbreviation(abbrev, def);
		state.p = p;
		return new MDMultiBlock([]);
	}
}

/**
 * Block reader for URL definitions. Links in the document can include a
 * reference instead of a verbatim URL so it can be defined in one place and
 * reused in many places. These can be defined anywhere in the document. Nothing
 * of the definition is rendered in the document.
 * 
 * Example:
 * 
 * > ```markdown
 * > [foo]: https://example.com
 * > ```
 */
class MDURLDefinitionBlockReader extends MDBlockReader {
	constructor(priority=50.0) {
		super(priority);
	}

	readBlock(state) {
		var p = state.p;
		let line = state.lines[p++];
		var symbol;
		var url;
		var title = null;
		let groups = /^\s*\[(.+?)]:\s*(\S+)\s+"(.*?)"\s*$/.exec(line);
		if (groups) {
			symbol = groups[1];
			url = groups[2];
			title = groups[3];
		} else {
			groups = /^\s*\[(.+?)]:\s*(\S+)\s*$/.exec(line);
			if (groups) {
				symbol = groups[1];
				url = groups[2];
			} else {
				return null;
			}
		}
		state.defineURL(symbol, url, title);
		state.p = p;
		return new MDInlineBlock([]);
	}
}

/**
 * Block reader for simple paragraphs. Paragraphs are separated by a blank (or
 * whitespace-only) line. This reader should be prioritized last since there
 * is no distinguishing syntax.
 * 
 * Example:
 * 
 * > ```markdown
 * > Lorem ipsum dolor
 * > sit amet. This is all one paragraph.
 * >
 * > Beginning of a new paragraph.
 * > ```
 */
class MDParagraphBlockReader extends MDBlockReader {
	constructor(priority=100.0) {
		super(priority);
	}

	readBlock(state) {
		var paragraphLines = [];
		var p = state.p;
		var foundBlankLine = false;
		while (p < state.lines.length) {
			let line = state.lines[p++];
			if (line.trim().length == 0) {
				foundBlankLine = true;
				break;
			}
			paragraphLines.push(line);
		}
		if (state.p == 0 && p >= state.lines.length) {
			// If it's the entire document don't wrap it in a paragraph
			return null;
		}
		if (paragraphLines.length > 0) {
			state.p = p;
			let content = paragraphLines.join("\n");
			return new MDParagraphBlock(new MDInlineBlock(state.inlineMarkdownToSpans(content)));
		}
		return null;
	}
}


// -- Inline reader ---------------------------------------------------------


class MDInlineReader {
	/** @type {number} */
	#tokenizePriority;

	/** @type {number|number[]} */
	#substitutePriority;

	/**
	 * A unitless relative tokenizing priority value that determines which
	 * readers are tried first. Lower values are tried first. Standard readers
	 * are in the range of 0.0 to 100.0 but any value is valid. Longer
	 * tokens should generally be prioritized over short or single character tokens.
	 * 
	 * @returns {number} priority or priorities for tokenization
	 */
	get tokenizePriority() { return this.#tokenizePriority; }

	/**
	 * A unitless relative substitution priority value that determines which
	 * readers are tried first. Lower values are tried first. If an array of
	 * values is given, the same reader will be included twice in the
	 * prioritization. This allows for multiple passes. Standard readers
	 * are in the range of 0.0 to 100.0 but any value is valid. Priority should
	 * be used to help resolve ambiguous parsings, with longer, more complex
	 * constructions best prioritized before shorter, simpler ones.
	 * 
	 * @returns {number|number[]} priority or priorities for substitution
	 */
	get substitutePriority() { return this.#substitutePriority; }

	/**
	 * @param {number} tokenizePriority
	 * @param {number|number[]} substitutePriority
	 */
	constructor(tokenizePriority, substitutePriority) {
		this.#tokenizePriority = tokenizePriority;
		this.#substitutePriority = substitutePriority;
	}

	/**
	 * Attempts to read a token from the start of the given string.
	 *
	 * @param {string} remainingText - remainder of the current line of markdown text left to tokenize
	 * @returns {MDToken|null} a token or `null` if not found
	 */
	readFirstToken(state, priority, remainingText) {
		throw new Error(`Abstract readFirstToken must be overridden in ${this.constructor.name}`);
	}

	/**
	 * Attempts to substitute one or more tokens in the given array. The given
	 * array is edited in-place via `.splice` operations. It consists of mixed
	 * elements of unprocessed `MDToken` and interpreted `MDSpan` elements.
	 * 
	 * If a structure consists of inner content that is also markdown encoded,
	 * those elements can be passed to `state.tokensToSpans` to resolve to an
	 * array of `MDSpan` elements.
	 *
	 * @param {MDState} state
	 * @param {number} priority - used to differentiate passes when multiple
	 *   values of `this.substitutePriority` are given
	 * @param {MDToken[]|MDSpan[]} tokens - mixed array of `MDToken` and
	 *   `MDSpan` elements to be modified by reference
	 * @returns {boolean} `true` if any substitutions were made; `false` if not
	 */
	substituteTokens(state, priority, tokens) {
		throw new Error(`Abstract substituteTokens must be overridden in ${this.constructor.name}`);
	}

	/**
	 * Called after the full document has been generated for optional
	 * post-processing.
	 *
	 * @param {MDState} state
	 * @param {MDBlock[]} blocks - top-level document block list
	 */
	postProcess(state, blocks) {
		// no op
	}
}

/**
 * Abstract base class for readers that look for one or more delimiting tokens
 * around some content.
 */
class MDSimplePairInlineReader extends MDInlineReader {
	constructor(tokenizePriority, substitutePriority) {
		super(tokenizePriority, substitutePriority);
	}

	/**
	 * Attempts a substitution of a matched pair of delimiting token types.
	 * If successful, the substitution is performed on `tokens` and `true` is
	 * returned, otherwise `false` is returned and the array is untouched.
	 * 
	 * If multiple `substitutePriority` values are specified, the first pass
	 * will reject matches with the delimiting character inside the content
	 * tokens. If a single `substitutePriority` is given or a subsequent pass
	 * is performed with multiple values any contents will be accepted.
	 * 
	 * @param {MDState} state
	 * @param {number} priority
	 * @param {MDToken[]} tokens
	 * @param {class} spanClass
	 * @param {MDTokenType} delimiter
	 * @param {number} count - how many times the token is repeated to form the delimiter
	 * @returns {boolean} `true` if substitution performed, `false` if not
	 */
	attemptPair(state, priority, tokens, spanClass, delimiter, count=1, plaintext=false) {
		let delimiters = Array(count).fill(delimiter);
		let firstPassPriority = (this.substitutePriority instanceof Array) ? this.substitutePriority[0] : null;
		let match = MDToken.findPairedTokens(tokens, delimiters, delimiters, function(content) {
			const firstType = content[0] instanceof MDToken ? content[0].type : null;
			const lastType = content[content.length - 1] instanceof MDToken ? content[content.length - 1].type : null;
			if (firstType == MDTokenType.Whitespace) return false;
			if (lastType == MDTokenType.Whitespace) return false;
			if (priority == firstPassPriority) {
				var innerCount = 0;
				for (let token of content) {
					if (token instanceof MDToken && token.type == delimiter) innerCount++;
				}
				if ((innerCount % 2) != 0) return false;
			}
			return true;
		});
		if (match === null) return false;
		let content = (plaintext)
			? match.contentTokens.map((token) => token.original).join('')
			: state.tokensToSpans(match.contentTokens);
		tokens.splice(match.startIndex, match.totalLength, new spanClass(content));
		return true;
	}
}

class MDStrongInlineReader extends MDSimplePairInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=[0.0, 50.0]) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		if (remainingText.startsWith('*')) return new MDToken('*', MDTokenType.Asterisk);
		if (remainingText.startsWith('_')) return new MDToken('_', MDTokenType.Underscore);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		if (this.attemptPair(state, priority, tokens, MDStrongSpan, MDTokenType.Asterisk, 2)) return true;
		if (this.attemptPair(state, priority, tokens, MDStrongSpan, MDTokenType.Underscore, 2)) return true;
		return false;
	}
}

class MDEmphasisInlineReader extends MDSimplePairInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=[0.0, 50.0]) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		if (remainingText.startsWith('*')) return new MDToken('*', MDTokenType.Asterisk);
		if (remainingText.startsWith('_')) return new MDToken('_', MDTokenType.Underscore);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		if (this.attemptPair(state, priority, tokens, MDEmphasisSpan, MDTokenType.Asterisk)) return true;
		if (this.attemptPair(state, priority, tokens, MDEmphasisSpan, MDTokenType.Underscore)) return true;
		return false;
	}
}

class MDCodeInlineReader extends MDSimplePairInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=0.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		if (remainingText.startsWith('`')) return new MDToken('`', MDTokenType.Backtick);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		// ignore priority
		if (this.attemptPair(state, -1, tokens, MDCodeSpan, MDTokenType.Backtick, 2, true)) return true;
		if (this.attemptPair(state, -1, tokens, MDCodeSpan, MDTokenType.Backtick, 1, true)) return true;
		return false;
	}
}

class MDStrikethroughInlineReader extends MDSimplePairInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=[0.0, 50.0]) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		if (remainingText.startsWith('~')) return new MDToken('~', MDTokenType.Tilde);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		if (this.attemptPair(state, priority, tokens, MDStrikethroughSpan, MDTokenType.Tilde, 2)) return true;
		if (this.attemptPair(state, priority, tokens, MDStrikethroughSpan, MDTokenType.Tilde)) return true;
		return false;
	}
}

class MDImageInlineReader extends MDInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=0.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		if (remainingText.startsWith('!')) return new MDToken('!', MDTokenType.Bang);
		var groups;
		if (groups = MDUtils.tokenizeLabel(remainingText)) {
			return new MDToken(groups[0], MDTokenType.Label, groups[1]);
		}
		if (groups = MDUtils.tokenizeURL(remainingText)) {
			return new MDToken(groups[0], MDTokenType.URL, groups[1], groups[2]);
		}
		return null;
	}

	substituteTokens(state, priority, tokens) {
		var match;
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Bang, MDTokenType.Label, MDTokenType.META_OptionalWhitespace, MDTokenType.URL ])) {
			let alt = match.tokens[1].content;
			let url = match.tokens[match.tokens.length - 1].content;
			let title = match.tokens[match.tokens.length - 1].extra;
			tokens.splice(match.index, match.tokens.length, new MDImageSpan(url, alt, title));
			return true;
		}
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Bang, MDTokenType.Label, MDTokenType.META_OptionalWhitespace, MDTokenType.Label ])) {
			let alt = match.tokens[1].content;
			let ref = match.tokens[match.tokens.length - 1].content;
			tokens.splice(match.index, match.tokens.length, new MDReferencedImageSpan(ref, alt));
			return true;
		}
		return false;
	}
}

class MDFootnoteInlineReader extends MDInlineReader {
	static #footnoteWithTitleRegex = /^\[\^([^\]]+?)\s+"(.*?)"\]/;  // 1=symbol, 2=title
	static #footnoteRegex = /^\[\^([^\]]+?)\]/;  // 1=symbol

	constructor(tokenizePriority=0.0, substitutePriority=0.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		var groups;
		if (groups = MDFootnoteInlineReader.#footnoteWithTitleRegex.exec(remainingText)) {
			return new MDToken(groups[0], MDTokenType.Footnote, groups[1], groups[2]);
		}
		if (groups = MDFootnoteInlineReader.#footnoteRegex.exec(remainingText)) {
			return new MDToken(groups[0], MDTokenType.Footnote, groups[1]);
		}
		return null;
	}

	substituteTokens(state, priority, tokens) {
		var match;
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Footnote ])) {
			let footnoteToken = match.tokens[0];
			tokens.splice(match.index, 1, new MDFootnoteReferenceSpan(footnoteToken.content));
			return true;
		}
		return false;
	}

	/**
	 * @param {MDState} state
	 * @param {MDBlock[]} blocks
	 */
	postProcess(state, blocks) {
		var unique = 1;
		for (const block of blocks) {
			block.visitChildren(function(node) {
				if (!(node instanceof MDFootnoteReferenceSpan)) return;
				node.differentiator = unique++;
				state.registerUniqueFootnote(node.symbol, node.differentiator);
			});
		}
		if (Object.keys(state.footnotes).length == 0) return;
		blocks.push(new MDFootnoteListingBlock());
	}
}

class MDLinkInlineReader extends MDInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=0.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		var groups;
		if (groups = MDUtils.tokenizeLabel(remainingText)) {
			return new MDToken(groups[0], MDTokenType.Label, groups[1]);
		}
		if (groups = MDUtils.tokenizeEmail(remainingText)) {
			return new MDToken(groups[0], MDTokenType.Email, groups[1], groups[2]);
		}
		if (groups = MDUtils.tokenizeURL(remainingText)) {
			return new MDToken(groups[0], MDTokenType.URL, groups[1], groups[2]);
		}
		return null;
	}

	/**
	 * @param {MDState} state
	 */
	substituteTokens(state, priority, tokens) {
		var match;
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Label, MDTokenType.META_OptionalWhitespace, MDTokenType.URL ])) {
			let text = match.tokens[0].content;
			let url = match.tokens[match.tokens.length - 1].content;
			let title = match.tokens[match.tokens.length - 1].extra;
			tokens.splice(match.index, match.tokens.length, new MDLinkSpan(url, state.inlineMarkdownToSpan(text), title));
			return true;
		}
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Label, MDTokenType.META_OptionalWhitespace, MDTokenType.Email ])) {
			let text = match.tokens[0].content;
			let email = match.tokens[match.tokens.length - 1].content;
			let url = `mailto:${email}`;
			let title = match.tokens[match.tokens.length - 1].extra;
			tokens.splice(match.index, match.tokens.length, new MDLinkSpan(url, state.inlineMarkdownToSpan(text), title));
			return true;
		}
		if (match = MDToken.findFirstTokens(tokens, [ MDTokenType.Label, MDTokenType.META_OptionalWhitespace, MDTokenType.Label ])) {
			let text = match.tokens[0].content;
			let ref = match.tokens[match.tokens.length - 1].content;
			tokens.splice(match.index, match.tokens.length, new MDReferencedLinkSpan(ref, state.inlineMarkdownToSpan(text)));
			return true;
		}
		return false;
	}
}

class MDSimpleLinkInlineReader extends MDInlineReader {
	static #simpleEmailRegex = new RegExp("^<(" + MDUtils.baseEmailRegex.source + ")>", "i");  // 1=email
	static #simpleURLRegex = new RegExp("^<(" + MDUtils.baseURLRegex.source + ")>", "i");  // 1=URL

	constructor(tokenizePriority=0.0, substitutePriority=0.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		var groups;
		if (groups = MDSimpleLinkInlineReader.#simpleEmailRegex.exec(remainingText)) {
			return new MDToken(groups[0], MDTokenType.SimpleEmail, groups[1]);
		}
		if (groups = MDSimpleLinkInlineReader.#simpleURLRegex.exec(remainingText)) {
			return new MDToken(groups[0], MDTokenType.SimpleLink, groups[1]);
		}
		return null;
	}

	#substituteEmail(state, tokens) {
		const result = MDToken.findFirstTokens(tokens, [ MDTokenType.SimpleEmail ]);
		if (result === null) return false;
		/** @type {MDToken} */
		const token = result.tokens[0];
		const link = `mailto:${token.content}`;
		const span = new MDLinkSpan(link, new MDObfuscatedTextSpan(token.content));
		tokens.splice(result.index, 1, span);
		return true;
	}

	#substituteURL(state, tokens) {
		const result = MDToken.findFirstTokens(tokens, [ MDTokenType.SimpleLink ]);
		if (result === null) return false;
		/** @type {MDToken} */
		const token = result.tokens[0];
		const link = token.content;
		const span = new MDLinkSpan(link, new MDTextSpan(link));
		tokens.splice(result.index, 1, span);
		return true;
	}

	substituteTokens(state, priority, tokens) {
		if (this.#substituteEmail(state, tokens)) return true;
		if (this.#substituteURL(state, tokens)) return true;
		return false;
	}
}

class MDHTMLTagInlineReader extends MDInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=95.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		var tag = MDHTMLTag.fromLineStart(remainingText);
		if (tag) return new MDToken(tag.fullTag, MDTokenType.HTMLTag, tag.fullTag, null, tag);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		const result = MDToken.findFirstTokens(tokens, [ MDTokenType.HTMLTag ]);
		if (result === null) return false;
		/** @type {MDToken} */
		const token = result.tokens[0];
		const tag = token.tag;
		const span = new MDHTMLSpan(tag);
		tokens.splice(result.index, 1, span);
		return true;
	}
}

class MDModifierInlineReader extends MDInlineReader {
	constructor(tokenizePriority=0.0, substitutePriority=100.0) {
		super(tokenizePriority, substitutePriority);
	}

	readFirstToken(state, priority, remainingText) {
		var modifier = MDTagModifier.fromStart(remainingText);
		if (modifier) return new MDToken(modifier.original, MDTokenType.Modifier, modifier);
		return null;
	}

	substituteTokens(state, priority, tokens) {
		// Modifiers are applied elsewhere, and if they're not it's fine if they're
		// rendered as the original syntax.
		return false;
	}
}


// -- Blocks ----------------------------------------------------------------


class MDBlock {
	/** @type {string[]} */
	cssClasses = [];
	/** @type {string|null} */
	cssId = null;
	/** @type {object} */
	attributes = {};

	/**
	 * @param {MDState} state
	 * @returns {string}
	 */
	toHTML(state) {
		throw new Error(`Abstract ${this.constructor.name}.toHTML must be implemented`);
	}

	/**
	 * @param {MDState} state
	 * @returns {string}
	 */
	toPlaintext(state) {
		throw new Error(`Abstract ${this.constructor.name}.toPlaintext must be implemented`);
	}

	htmlAttributes() {
		var html = '';
		if (this.cssClasses.length > 0) {
			html += ` class="${this.cssClasses.join(' ')}"`;
		}
		if (this.cssId !== null) {
			html += ` id="${this.cssId}"`;
		}
		for (const name in this.attributes) {
			let value = this.attributes[name];
			html += ` ${name}="${MDUtils.escapeHTML(value)}"`;
		}
		return html;
	}

	/**
	 * @param {MDBlock[]} blocks
	 * @param {MDState} state
	 * @returns {string}
	 */
	static toHTML(blocks, state) {
		return blocks.map((block) => block.toHTML(state)).join("\n");
	}

	/**
	 * @param {MDBlock[]} blocks
	 * @param {MDState} state
	 * @returns {string}
	 */
	static toPlaintext(blocks, state) {
		return blocks.map((block) => block.toPlaintext(state)).join("\n");
	}

	/**
	 * Visits all block and inline children of this block, calling the given
	 * function with each. Should be implemented for any block with child nodes.
	 *
	 * @param {function} fn
	 */
	visitChildren(fn) {}
}

class MDMultiBlock extends MDBlock {
	/** @type {MDBlock[]} */
	blocks;

	/**
	 * @param {MDBlock[]} blocks
	 */
	constructor(blocks) {
		super();
		if (blocks instanceof Array) {
			this.blocks = blocks;
		} else {
			throw new Error(`${MDUtils.typename(this)} expects MDBlock[], got ${MDUtils.typename(blocks)}`);
		}
	}

	toHTML(state) {
		return MDBlock.toHTML(this.blocks, state);
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.blocks, state);
	}

	visitChildren(fn) {
		for (const block of this.blocks) {
			fn(block);
			block.visitChildren(fn);
		}
	}
}

class MDParagraphBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {MDBlock|MDBlock[]} content
	 */
	constructor(content) {
		super();
		if (content instanceof Array) {
			this.content = content;
		} else if (content instanceof MDBlock) {
			this.content = [ content ];
		} else {
			throw new Error(`${MDUtils.typename(this)} expects MDBlock[] or MDBlock, got ${MDUtils.typename(content)}`);
		}
	}

	toHTML(state) {
		const contentHTML = MDBlock.toHTML(this.content, state);
		return `<p${this.htmlAttributes()}>${contentHTML}</p>\n`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const child of this.content) {
			fn(child);
			child.visitChildren(fn);
		}
	}
}

class MDHeaderBlock extends MDBlock {
	/** @type {number} */
	level;
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {number} level
	 * @param {MDBlock|MDBlock[]} content
	 */
	constructor(level, content) {
		super();
		this.level = level;
		this.content = (content instanceof Array) ? content : [ content ];
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<h${this.level}${this.htmlAttributes()}>${contentHTML}</h${this.level}>\n`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const child of this.content) {
			fn(child);
			child.visitChildren(fn);
		}
	}
}

class MDBlockquoteBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {MDBlock|MDBlock[]} content
	 */
	constructor(content) {
		super();
		this.content = (content instanceof MDBlock) ? [ content ] : content;
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<blockquote${this.htmlAttributes()}>\n${contentHTML}\n</blockquote>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const block of this.content) {
			fn(block);
			block.visitChildren(fn);
		}
	}
}

class MDUnorderedListBlock extends MDBlock {
	/** @type {MDListItemBlock[]} */
	items;

	/**
	 * @param {MDListItemBlock[]} items
	 */
	constructor(items) {
		super();
		this.items = items;
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.items, state);
		return `<ul${this.htmlAttributes()}>\n${contentHTML}\n</ul>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.items, state);
	}

	visitChildren(fn) {
		for (const item of this.items) {
			fn(item);
			item.visitChildren(fn);
		}
	}
}

class MDOrderedListBlock extends MDBlock {
	/** @type {MDListItemBlock[]} */
	items;

	/** @type {number|null} */
	startOrdinal;

	/**
	 * @param {MDListItemBlock[]} items
	 */
	constructor(items, startOrdinal=null) {
		super();
		this.items = items;
		this.startOrdinal = startOrdinal;
	}

	htmlAttributes() {
		var html = super.htmlAttributes();
		if (this.startOrdinal !== null && this.startOrdinal != 1) {
			html += ` start="${this.startOrdinal}"`;
		}
		return html;
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.items, state);
		return `<ol${this.htmlAttributes()}>\n${contentHTML}\n</ol>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.items, state);
	}

	visitChildren(fn) {
		for (const item of this.items) {
			fn(item);
			item.visitChildren(fn);
		}
	}
}

class MDListItemBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;
	/** @type {number|null} */
	ordinal;

	/**
	 * @param {MDBlock|MDBlock[]} content
	 * @param {number|null} ordinal
	 */
	constructor(content, ordinal=null) {
		super();
		if (content instanceof Array) {
			this.content = content;
		} else {
			this.content = [ content ];
		}
		this.ordinal = ordinal;
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<li${this.htmlAttributes()}>${contentHTML}</li>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const child of this.content) {
			fn(child);
			child.visitChildren(fn);
		}
	}
}

class MDCodeBlock extends MDBlock {
	/** @type {string} */
	code;

	/**
	 * @param {string} code
	 */
	constructor(code) {
		super();
		this.code = code;
	}

	toHTML(state) {
		return `<pre${this.htmlAttributes()}><code>${MDUtils.escapeHTML(this.code)}</code></pre>`;
	}

	toPlaintext(state) {
		return this.code;
	}
}

class MDHorizontalRuleBlock extends MDBlock {
	toHTML(state) {
		return `<hr${this.htmlAttributes()}>\n`;
	}

	toPlaintext(state) {
		return '';
	}
}

class MDTableCellBlock extends MDBlock {
	static AlignLeft = 'left';
	static AlignCenter = 'center';
	static AlignRight = 'right';

	/** @type {MDBlock} */
	content;
	/** @type {string|null} */
	align = null;

	/**
	 * @param {MDBlock} content
	 */
	constructor(content) {
		super();
		this.content = content;
	}

	#alignAttribute() {
		switch (this.align) {
			case MDTableCellBlock.AlignLeft: return ' align="left"';
			case MDTableCellBlock.AlignCenter: return ' align="center"';
			case MDTableCellBlock.AlignRight: return ' align="right"';
			default: return '';
		}
	}

	htmlAttributes() {
		var html = super.htmlAttributes();
		html += this.#alignAttribute();
		return html;
	}

	toHTML(state) {
		let contentHTML = this.content.toHTML(state);
		return `<td${this.htmlAttributes()}>${contentHTML}</td>`;
	}

	toPlaintext(state) {
		return this.content.toPlaintext(state);
	}

	visitChildren(fn) {
		fn(this.content);
		this.content.visitChildren(fn);
	}
}

class MDTableHeaderCellBlock extends MDTableCellBlock {
	toHTML(state) {
		let html = super.toHTML(state);
		let groups = /^<td(.*)td>$/.exec(html);
		return `<th${groups[1]}th>`;
	}
}

class MDTableRowBlock extends MDBlock {
	/** @type {MDTableCellBlock[]|MDTableHeaderCellBlock[]} */
	cells;

	/**
	 * @param {MDTableCellBlock[]|MDTableHeaderCellBlock[]} cells
	 */
	constructor(cells) {
		super();
		this.cells = cells;
	}

	/**
	 * @param {string[]} alignments
	 */
	applyAlignments(alignments) {
		for (var i = 0; i < this.cells.length; i++) {
			let cell = this.cells[i];
			let align = i < alignments.length ? alignments[i] : null;
			cell.align = align;
		}
	}

	toHTML(state) {
		let cellsHTML = MDBlock.toHTML(this.cells, state);
		return `<tr${this.htmlAttributes()}>\n${cellsHTML}\n</tr>`;
	}

	toPlaintext(state) {
		return this.cells.map((cell) => cell.toPlaintext(state)).join(' ');
	}

	visitChildren(fn) {
		for (const cell of this.cells) {
			fn(cell);
			cell.visitChildren(fn);
		}
	}
}

class MDTableBlock extends MDBlock {
	/** @type {MDTableRowBlock} */
	headerRow;
	/** @type {MDTableRowBlock[]} */
	bodyRows;

	/**
	 * @param {MDTableRowBlock} headerRow
	 * @param {MDTableRowBlock[]} bodyRows
	 */
	constructor(headerRow, bodyRows) {
		super();
		this.headerRow = headerRow;
		this.bodyRows = bodyRows;
	}

	toHTML(state) {
		let headerRowHTML = this.headerRow.toHTML(state);
		let bodyRowsHTML = MDBlock.toHTML(this.bodyRows, state);
		return `<table${this.htmlAttributes()}>\n<thead>\n${headerRowHTML}\n</thead>\n<tbody>\n${bodyRowsHTML}\n</tbody>\n</table>`;
	}

	toPlaintext(state) {
		return this.headerRow.toPlaintext(state) + "\n" + this.bodyRows.map((row) => row.toPlaintext(state)).join("\n");
	}

	visitChildren(fn) {
		fn(this.headerRow);
		this.headerRow.visitChildren(fn);
		for (const row of this.bodyRows) {
			fn(row);
			row.visitChildren(fn);
		}
	}
}

class MDDefinitionListBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {MDBlock[]} content
	 */
	constructor(content) {
		super();
		this.content = content;
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<dl${this.htmlAttributes()}>\n${contentHTML}\n</dl>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const block of this.content) {
			fn(block);
			block.visitChildren(fn);
		}
	}
}

class MDDefinitionTermBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {MDBlock|MDBlock[]} content
	 */
	constructor(content) {
		super();
		if (content instanceof Array) {
			this.content = content;
		} else if (content instanceof MDBlock) {
			this.content = [ content ];
		} else {
			throw new Error(`${this.constructor.name} expects MDBlock or MDBlock[], got ${typeof content}`);
		}
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<dt${this.htmlAttributes()}>${contentHTML}</dt>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const child of this.content) {
			fn(child);
			child.visitChildren(fn);
		}
	}
}

class MDDefinitionDefinitionBlock extends MDBlock {
	/** @type {MDBlock[]} */
	content;

	/**
	 * @param {MDBlock|MDBlock[]} content
	 */
	constructor(content) {
		super();
		if (content instanceof Array) {
			this.content = content;
		} else if (content instanceof MDBlock) {
			this.content = [ content ];
		} else {
			throw new Error(`${this.constructor.name} expects MDBlock or MDBlock[], got ${typeof content}`);
		}
	}

	toHTML(state) {
		let contentHTML = MDBlock.toHTML(this.content, state);
		return `<dd${this.htmlAttributes()}>${contentHTML}</dd>`;
	}

	toPlaintext(state) {
		return MDBlock.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const child of this.content) {
			fn(child);
			child.visitChildren(fn);
		}
	}
}

class MDFootnoteListingBlock extends MDBlock {
	constructor() {
		super();
	}

	/**
	 * @param {MDState} state
	 */
	toHTML(state) {
		const footnotes = state.footnotes;
		var symbolOrder = Object.keys(footnotes);
		if (Object.keys(footnotes).length == 0) return '';
		const footnoteUniques = state.footnoteInstances;
		var html = '';
		html += '<div class="footnotes"><hr/>';
		html += '<ol>';
		for (const symbol of symbolOrder) {
			/** @type {MDBlock} */
			let content = footnotes[symbol];
			if (!content) continue;
			html += `<li value="${symbol}" id="footnote_${symbol}">${content.toHTML(state)}`;
			for (const unique of footnoteUniques[symbol]) {
				html += ` <a href="#footnoteref_${unique}" class="footnote-backref">↩︎</a>`;
			}
			html += `</li>\n`;
		}
		html += '</ol>';
		html += '</div>';
		return html;
	}

	toPlaintext(state) {
		const footnotes = state.footnotes;
		var symbolOrder = Object.keys(footnotes);
		if (Object.keys(footnotes).length == 0) return '';
		var text = '';
		for (const symbol of symbolOrder) {
			let content = footnotes[symbol];
			if (!content) continue;
			text += `${symbol}. ${content.toPlaintext(state)}\n`;
		}
		return text.trim();
	}
}

class MDInlineBlock extends MDBlock {
	/** @type {MDSpan[]} */
	content;

	/**
	 * @param {MDSpan|MDSpan[]} content
	 */
	constructor(content) {
		super();
		this.content = (content instanceof Array) ? content : [ content ];
		for (const span of this.content) {
			if (!(span instanceof MDSpan)) {
				throw new Error(`${this.constructor.name} expects MDSpan or MDSpan[], got ${MDUtils.typename(span)}`);
			}
		}
	}

	toHTML(state) {
		return MDSpan.toHTML(this.content, state);
	}

	toPlaintext(state) {
		return MDSpan.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const span of this.content) {
			fn(span);
			span.visitChildren(fn);
		}
	}
}

// -- Spans -----------------------------------------------------------------


class MDSpan {
	/** @type {string[]} */
	cssClasses = [];
	/** @type {string|null} */
	cssId = null;
	/** @type {object} */
	attributes = {};

	/**
	 * @param {MDState} state
	 * @returns {string} HTML
	 */
	toHTML(state) {
		throw new Error(`Abstract ${this.constructor.name}.toHTML must be implemented`);
	}

	toPlaintext(state) {
		throw new Error(`Abstract ${this.constructor.name}.toPlaintext must be implemented`);
	}

	htmlAttributes() {
		var html = '';
		if (this.cssClasses.length > 0) {
			html += ` class="${this.cssClasses.join(' ')}"`;
		}
		if (this.cssId !== null) {
			html += ` id="${this.cssId}"`;
		}
		for (const name in this.attributes) {
			let value = this.attributes[name];
			html += ` ${name}="${MDUtils.escapeHTML(value)}"`;
		}
		return html;
	}

	/**
	 * @param {MDSpan[]} spans
	 * @param {MDState} state
	 * @returns {string}
	 */
	static toHTML(spans, state) {
		return spans.map((span) => span.toHTML(state)).join('');
	}

	/**
	 * @param {MDSpan[]} spans
	 * @param {MDState} state
	 * @returns {string}
	 */
	static toPlaintext(spans, state) {
		return spans.map((span) => span.toPlaintext(state)).join('');
	}

	/**
	 * Visits all inline children of this span, calling the given function with
	 * each. Should be implemented for any span with child nodes.
	 *
	 * @param {function} fn
	 */
	visitChildren(fn) {}
}

class MDMultiSpan extends MDSpan {
	/** @type {MDSpan[]} */
	content;

	/**
	 * @param {MDSpan[]} content
	 */
	constructor(content) {
		super();
		this.content = content;
	}

	toHTML(state) {
		return MDSpan.toHTML(this.content, state);
	}

	toPlaintext(state) {
		return MDSpan.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const span of this.content) {
			fn(span);
			span.visitChildren(fn);
		}
	}
}

class MDTextSpan extends MDSpan {
	/** @param {string} text */
	text;

	/**
	 * @param {string} text
	 */
	constructor(text) {
		super();
		this.text = text;
	}

	toHTML(state) {
		let html = MDUtils.escapeHTML(this.text);
		let abbrevs = state.abbreviations;
		let regexes = state.abbreviationRegexes;
		for (const abbrev in abbrevs) {
			let def = abbrevs[abbrev];
			let regex = regexes[abbrev];
			let escapedDef = MDUtils.escapeHTML(def);
			html = html.replace(regex, `<abbr title="${escapedDef}">$1</abbr>`);
		}
		return html;
	}

	toPlaintext(state) {
		return this.text;
	}
}

class MDHTMLSpan extends MDSpan {
	/** @param {string} */
	tag;

	/**
	 * @param {MDHTMLTag} tag
	 */
	constructor(tag) {
		super();
		this.tag = tag;
	}

	toHTML(state) {
		return this.tag.fullTag;
	}

	toPlaintext(state) {
		return '';
	}
}

class MDObfuscatedTextSpan extends MDSpan {
	/** @param {string} text */
	text;

	/**
	 * @param {string} text
	 */
	constructor(text) {
		super();
		this.text = text;
	}

	toHTML(state) {
		return MDUtils.escapeObfuscated(this.text);
	}

	toPlaintext(state) {
		return this.text;
	}
}

class MDLinkSpan extends MDSpan {
	/** @type {string} */
	link;
	/** @type {string|null} */
	target = null;
	/** @type {MDSpan} */
	content;
	/** @type {string|null} */
	title = null;

	/**
	 * @param {string} link
	 * @param {MDSpan} content
	 * @param {string|null} title
	 */
	constructor(link, content, title=null) {
		super();
		this.link = link;
		this.content = content;
		this.title = title;
	}

	toHTML(state) {
		var escapedLink;
		if (this.link.startsWith('mailto:')) {
			escapedLink = 'mailto:' + MDUtils.escapeObfuscated(this.link.substring(7));
		} else {
			escapedLink = MDUtils.escapeHTML(this.link);
		}
		var html = `<a href="${escapedLink}"`;
		if (this.target) {
			html += ` target="${MDUtils.escapeHTML(this.target)}"`;
		}
		if (this.title) {
			html += ` title="${MDUtils.escapeHTML(this.title)}"`;
		}
		html += this.htmlAttributes();
		html += '>' + this.content.toHTML(state) + '</a>';
		return html;
	}

	toPlaintext(state) {
		return this.content.toPlaintext(state);
	}

	visitChildren(fn) {
		fn(this.content);
		this.content.visitChildren(fn);
	}
}

class MDReferencedLinkSpan extends MDLinkSpan {
	/** @type {string} */
	ref;

	constructor(ref, content) {
		super(null, content, null);
		this.ref = ref;
	}

	/**
	 * @param {MDState} state
	 */
	toHTML(state) {
		if (!this.link) {
			let url = state.urls[this.ref.toLowerCase()];
			let title = state.urlTitles[this.ref.toLowerCase()];
			this.link = url;
			this.title = title || this.title;
		}
		if (this.link) {
			return super.toHTML(state);
		} else {
			let contentHTML = this.content.toHTML(state);
			return `[${contentHTML}][${this.ref}]`;
		}
	}
}

class MDEmphasisSpan extends MDSpan {
	/** @type {MDSpan[]} */
	content;

	/**
	 * @param {MDSpan|MDSpan[]} content
	 */
	constructor(content) {
		super();
		this.content = (content instanceof MDSpan) ? [ content ] : content;
	}

	toHTML(state) {
		let contentHTML = MDSpan.toHTML(this.content, state);
		return `<em${this.htmlAttributes()}>${contentHTML}</em>`;
	}

	toPlaintext(state) {
		return MDSpan.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const span of this.content) {
			fn(span);
			span.visitChildren(fn);
		}
	}
}

class MDStrongSpan extends MDSpan {
	/** @type {MDSpan[]} content */
	content;

	/**
	 * @param {MDSpan|MDSpan[]} content
	 */
	constructor(content) {
		super();
		this.content = (content instanceof MDSpan) ? [content] : content;
	}

	toHTML(state) {
		let contentHTML = MDSpan.toHTML(this.content, state);
		return `<strong${this.htmlAttributes()}>${contentHTML}</strong>`;
	}

	toPlaintext(state) {
		return MDSpan.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const span of this.content) {
			fn(span);
			span.visitChildren(fn);
		}
	}
}

class MDStrikethroughSpan extends MDSpan {
	/** @type {MDSpan[]} content */
	content;

	/**
	 * @param {MDSpan|MDSpan[]} content
	 */
	constructor(content) {
		super();
		this.content = (content instanceof MDSpan) ? [content] : content;
	}

	toHTML(state) {
		let contentHTML = MDSpan.toHTML(this.content, state);
		return `<strike${this.htmlAttributes()}>${contentHTML}</strike>`;
	}

	toPlaintext(state) {
		return MDSpan.toPlaintext(this.content, state);
	}

	visitChildren(fn) {
		for (const span of this.content) {
			fn(span);
			span.visitChildren(fn);
		}
	}
}

class MDCodeSpan extends MDSpan {
	/** @type {String} content */
	content;

	/**
	 * @param {String} content
	 */
	constructor(content) {
		super();
		if (typeof content == 'string') {
			this.content = content;
		} else {
			throw new Error(`${this.constructor.name} content must be String, got ${typeof content}`);
		}
	}

	toHTML(state) {
		return `<code${this.htmlAttributes()}>${MDUtils.escapeHTML(this.content)}</code>`;
	}

	toPlaintext(state) {
		return this.content;
	}
}

class MDImageSpan extends MDSpan {
	/** @type {string} */
	source;
	/** @type {string|null} */
	alt;
	/** @type {string|null} */
	title;

	/**
	 * @param {string} source - image URL
	 * @param {string} alt - alt text
	 * @param {string|null} title - optional title attribute
	 */
	constructor(source, alt, title=null) {
		super();
		this.source = source;
		this.alt = alt;
		this.title = title;
	}

	toHTML(state) {
		let html = `<img src="${MDUtils.escapeHTML(this.source)}"`;
		if (this.alt) {
			html += ` alt="${MDUtils.escapeHTML(this.alt)}"`;
		}
		if (this.title) {
			html += ` title="${MDUtils.escapeHTML(this.title)}"`;
		}
		html += this.htmlAttributes();
		html += '>';
		return html;
	}

	toPlaintext(state) {
		return this.alt || '';
	}
}

class MDReferencedImageSpan extends MDImageSpan {
	/** @type {string} */
	ref;

	/**
	 * @param {string} ref
	 * @param {string|null} alt
	 */
	constructor(ref, alt) {
		super(null, alt);
		this.ref = ref;
	}

	toHTML(state) {
		if (!this.source) {
			let url = state.urls[this.ref.toLowerCase()];
			let title = state.urlTitles[this.ref.toLowerCase()];
			this.source = url;
			this.title = title || this.title;
		}
		if (this.source) {
			return super.toHTML(state);
		} else {
			return `![${MDUtils.escapeHTML(this.alt)}][${MDUtils.escapeHTML(this.ref)}]`;
		}
	}
}

class MDFootnoteReferenceSpan extends MDSpan {
	/** @type {string} */
	symbol;

	/** @type {number|null} */
	differentiator = null;

	/**
	 * @param {string} symbol
	 */
	constructor(symbol) {
		super();
		this.symbol = symbol;
	}

	toHTML(state) {
		if (this.differentiator !== null) {
			return `<sup id="footnoteref_${this.differentiator}"><a href="#footnote_${this.symbol}">${this.symbol}</a></sup>`;
		}
		return `<!--FNREF:{${this.symbol}}-->`;
	}

	toPlaintext(state) {
		return this.symbol;
	}
}


// -- Other -----------------------------------------------------------------


class MDHTMLTag {
	/** @type {string} */
	fullTag;
	/** @type {string} */
	tagName;
	/** @type {boolean} */
	isCloser;
	/** @type {object} */
	attributes;

	/**
	 * @param {string} fullTag
	 * @param {string} tagName
	 * @param {boolean} isCloser
	 * @param {object} attributes
	 */
	constructor(fullTag, tagName, isCloser, attributes) {
		this.fullTag = fullTag;
		this.tagName = tagName;
		this.isCloser = isCloser;
		this.attributes = attributes;
	}

	toString() {
		return this.fullTag;
	}

	equals(other) {
		if (!(other instanceof MDHTMLTag)) return false;
		return other.fullTag == this.fullTag;
	}

	static #htmlTagNameFirstRegex = /[a-z]/i;
	static #htmlTagNameMedialRegex = /[a-z0-9]/i;
	static #htmlAttributeNameFirstRegex = /[a-z]/i;
	static #htmlAttributeNameMedialRegex = /[a-z0-9-]/i;
	static #whitespaceCharRegex = /\s/;

	/**
	 * @param {string} line
	 * @returns {MDHTMLTag|null} HTML tag if possible
	 */
	static fromLineStart(line) {
		let expectOpenBracket = 0;
		let expectCloserOrName = 1;
		let expectName = 2;
		let expectAttributeNameOrEnd = 3;
		let expectEqualsOrAttributeOrEnd = 4;
		let expectAttributeValue = 5;
		let expectCloseBracket = 6;

		var isCloser = false;
		var tagName = '';
		var attributeName = '';
		var attributeValue = '';
		var attributeQuote = null;
		var attributes = {};
		var fullTag = null;
		let endAttribute = function() {
			if (attributeName.length > 0) {
				if (attributeValue.length > 0 || attributeQuote) {
					attributes[attributeName] = attributeValue;
				} else {
					attributes[attributeName] = true;
				}
			}
			attributeName = '';
			attributeValue = '';
			attributeQuote = null;
		};

		var expect = expectOpenBracket;
		for (var p = 0; p < line.length && fullTag === null; p++) {
			let ch = line.substring(p, p + 1);
			let isWhitespace = this.#whitespaceCharRegex.exec(ch) !== null;
			switch (expect) {
				case expectOpenBracket:
					if (ch != '<') return null;
					expect = expectCloserOrName;
					break;
				case expectCloserOrName:
					if (ch == '/') {
						isCloser = true;
					} else {
						p--;
					}
					expect = expectName;
					break;
				case expectName:
					if (tagName.length == 0) {
						if (this.#htmlTagNameFirstRegex.exec(ch) === null) return null;
						tagName += ch;
					} else {
						if (this.#htmlTagNameMedialRegex.exec(ch)) {
							tagName += ch;
						} else {
							p--;
							expect = (isCloser) ? expectCloseBracket : expectAttributeNameOrEnd;
						}
					}
					break;
				case expectAttributeNameOrEnd:
					if (attributeName.length == 0) {
						if (isWhitespace) {
							// skip whitespace
						} else if (ch == '/') {
							expect = expectCloseBracket;
						} else if (ch == '>') {
							fullTag = line.substring(0, p + 1);
							break;
						} else if (this.#htmlAttributeNameFirstRegex.exec(ch)) {
							attributeName += ch;
						} else {
							return null;
						}
					} else if (isWhitespace) {
						expect = expectEqualsOrAttributeOrEnd;
					} else if (ch == '/') {
						endAttribute();
						expect = expectCloseBracket;
					} else if (ch == '>') {
						endAttribute();
						fullTag = line.substring(0, p + 1);
						break;
					} else if (ch == '=') {
						expect = expectAttributeValue;
					} else if (this.#htmlAttributeNameMedialRegex.exec(ch)) {
						attributeName += ch;
					} else {
						return null;
					}
					break;
				case expectEqualsOrAttributeOrEnd:
					if (ch == '=') {
						expect = expectAttributeValue;
					} else if (isWhitespace) {
						// skip whitespace
					} else if (ch == '/') {
						expect = expectCloseBracket;
					} else if (ch == '>') {
						fullTag = line.substring(0, p + 1);
						break;
					} else if (this.#htmlAttributeNameFirstRegex.exec(ch)) {
						endAttribute();
						expect = expectAttributeNameOrEnd;
						p--;
					}
					break;
				case expectAttributeValue:
					if (attributeValue.length == 0) {
						if (attributeQuote === null) {
							if (isWhitespace) {
								// skip whitespace
							} else if (ch == '"' || ch == "'") {
								attributeQuote = ch;
							} else {
								attributeQuote = ''; // explicitly unquoted
								p--;
							}
						} else {
							if (ch === attributeQuote) {
								// Empty string
								endAttribute();
								expect = expectAttributeNameOrEnd;
							} else if (attributeQuote === '' && (ch == '/' || ch == '>')) {
								return null;
							} else {
								attributeValue += ch;
							}
						}
					} else {
						if (ch === attributeQuote) {
							endAttribute();
							expect = expectAttributeNameOrEnd;
						} else if (attributeQuote === '' && isWhitespace) {
							endAttribute();
							expect = expectAttributeNameOrEnd;
						} else {
							attributeValue += ch;
						}
					}
					break;
				case expectCloseBracket:
					if (isWhitespace) {
						// ignore whitespace
					} else if (ch == '>') {
						fullTag = line.substring(0, p + 1);
						break;
					}
					break;
			}
		}
		if (fullTag === null) return null;
		endAttribute();
		return new MDHTMLTag(fullTag, tagName, isCloser, attributes);
	}
}

class MDTagModifier {
	/** @type {string} */
	original;
	/** @type {string[]} */
	cssClasses = [];
	/** @type {string|null} */
	cssId = null;
	/** @type {object} */
	attributes = {};

	static #baseClassRegex = /\.([a-z_\-][a-z0-9_\-]*?)/i;
	static #baseIdRegex = /#([a-z_\-][a-z0-9_\-]*?)/i;
	static #baseAttributeRegex = /([a-z0-9]+?)=([^\s\}]+?)/i;
	static #baseRegex = /\{([^}]+?)}/i;
	static #leadingClassRegex = new RegExp('^' + this.#baseRegex.source, 'i');
	static #trailingClassRegex = new RegExp('^(.*?)\\s*' + this.#baseRegex.source + '\\s*$', 'i');
	static #classRegex = new RegExp('^' + this.#baseClassRegex.source + '$', 'i');  // 1=classname
	static #idRegex = new RegExp('^' + this.#baseIdRegex.source + '$', 'i');  // 1=id
	static #attributeRegex = new RegExp('^' + this.#baseAttributeRegex.source + '$', 'i');  // 1=attribute name, 2=attribute value

	/**
	 * @param {MDBlock|MDSpan} elem
	 */
	applyTo(elem) {
		if (elem instanceof MDBlock || elem instanceof MDSpan) {
			elem.cssClasses = elem.cssClasses.concat(this.cssClasses);
			if (this.cssId) elem.cssId = this.cssId;
			for (const name in this.attributes) {
				elem.attributes[name] = this.attributes[name];
			}
		}
	}

	equals(other) {
		if (!(other instanceof MDTagModifier)) return false;
		if (!MDUtils.equal(other.cssClasses, this.cssClasses)) return false;
		if (other.cssId !== this.cssId) return false;
		if (!MDUtils.equal(other.attributes, this.attributes)) return false;
		return true;
	}

	toString() {
		return this.original;
	}

	static #fromContents(contents) {
		let modifierTokens = contents.split(/\s+/);
		let mod = new MDTagModifier();
		mod.original = `{${contents}}`;
		var groups;
		for (const token of modifierTokens) {
			if (token.trim() == '') continue;
			if (groups = this.#classRegex.exec(token)) {
				mod.cssClasses.push(groups[1]);
			} else if (groups = this.#idRegex.exec(token)) {
				mod.cssId = groups[1];
			} else if (groups = this.#attributeRegex.exec(token)) {
				mod.attributes[groups[1]] = groups[2];
			} else {
				return null;
			}
		}
		return mod;
	}

	/**
	 * Extracts modifier from line.
	 * @param {string} line
	 * @returns {Array} Tuple with remaining line and MDTagModifier.
	 */
	static fromLine(line) {
		let groups = this.#trailingClassRegex.exec(line);
		if (groups === null) return [ line, null ];
		let bareLine = groups[1];
		let mod = this.#fromContents(groups[2]);
		return [ bareLine, mod ];
	}

	/**
	 * Extracts modifier from head of string.
	 * @param {string} line
	 * @returns {MDTagModifier}
	 */
	static fromStart(line) {
		let groups = this.#leadingClassRegex.exec(line);
		if (groups === null) return null;
		return this.#fromContents(groups[1]);
	}

	/**
	 * @param {string} line
	 * @returns {string}
	 */
	static strip(line) {
		let groups = this.#trailingClassRegex.exec(line);
		if (groups === null) return line;
		return groups[1];
	}
}

class MDState {
	/** @type {string[]} */
	#lines = [];

	/**
	 * Abbreviation string (case sensitive) -> definition string
	 * @type {object}
	 */
	#abbreviations = {};

	/**
	 * Abbreviation string (case sensitive) -> RegExp
	 * @type {object}
	 */
	#abbreviationRegexes = {};

	/**
	 * Footnote symbol string -> content MDBlock
	 * @type {object}
	 */
	#footnotes = {};

	/**
	 * Footnote symbol string -> unique number[]
	 * @type {object}
	 */
	#footnoteInstances = {};

	/**
	 * Reference symbol -> URL string
	 * @type {object}
	 */
	#urlDefinitions = {};

	/**
	 * Reference symbol -> title string
	 * @type {object}
	 */
	#urlTitles = {};

	/** @type {number} */
	p = 0;

	/** @type {MDState|null} */
	#parent = null;

	/**
	 * Block readers sorted by priority.
	 * @type {MDBlockReader[]} readers
	 */
	#blockReadersByPriority = [];

	/**
	 * Tuples of priority:number and MDInlineReader sorted by `tokenizePriority`.
	 * @type {Array}
	 */
	#inlineReadersByTokenPriority = [];

	/**
	 * Tuples of priority:number and MDInlineReader sorted by `substitutePriority`.
	 */
	#inlineReadersBySubstitutePriority = [];

	/** @returns {string[]} */
	get lines() { return this.#lines; }

	/** @returns {string|null} */
	get currentLine() { return (this.p < this.#lines.length) ? this.#lines[this.p] : null; }

	/** @returns {object} */
	get abbreviations() {
		return (this.#parent) ? this.#parent.abbreviations : this.#abbreviations;
	}

	/** @returns {object} */
	get abbreviationRegexes() {
		return (this.#parent) ? this.#parent.abbreviationRegexes : this.#abbreviationRegexes;
	}

	/** @returns {object} */
	get footnotes() {
		return (this.#parent) ? this.#parent.footnotes : this.#footnotes;
	}

	/** @returns {object} */
	get footnoteInstances() {
		return (this.#parent) ? this.#parent.footnoteInstances : this.#footnoteInstances;
	}

	/** @returns {object} */
	get urls() {
		return (this.#parent) ? this.#parent.urls : this.#urlDefinitions;
	}

	/** @returns {object} */
	get urlTitles() {
		return (this.#parent) ? this.#parent.urlTitles : this.#urlTitles;
	}

	/**
	 * Block readers sorted by priority.
	 * @type {MDBlockReader[]} readers
	 */
	get blockReadersByPriority() {
		return (this.#parent) ? this.#parent.blockReadersByPriority : this.#blockReadersByPriority;
	}
	set blockReadersByPriority(newValue) {
		this.#blockReadersByPriority = newValue;
	}

	/**
	 * Tuples of priority:number and MDInlineReader sorted by `tokenizePriority`.
	 * @type {Array}
	 */
	get inlineReadersByTokenPriority() {
		return (this.#parent) ? this.#parent.inlineReadersByTokenPriority : this.#inlineReadersByTokenPriority;
	}
	set inlineReadersByTokenPriority(newValue) {
		this.#inlineReadersByTokenPriority = newValue;
	}

	/**
	 * Tuples of priority:number and MDInlineReader sorted by `substitutePriority`.
	 */
	get inlineReadersBySubstitutePriority() {
		return (this.#parent) ? this.#parent.inlineReadersBySubstitutePriority : this.#inlineReadersBySubstitutePriority;
	}
	set inlineReadersBySubstitutePriority(newValue) {
		this.#inlineReadersBySubstitutePriority = newValue;
	}

	/**
	 * @param {string[]} lines
	 */
	constructor(lines) {
		this.#lines = lines;
	}

	/**
	 * Creates a copy of this state with new lines. Useful for parsing nested
	 * content.
	 *
	 * @param {string[]} lines
	 * @returns {MDState} copied sub-state
	 */
	copy(lines) {
		let cp = new MDState(lines);
		cp.#parent = this;
		return cp;
	}

	/**
	 * Defines an abbreviation.
	 *
	 * @param {string} abbreviation - case sensitive
	 * @param {string} definition - brief definition of the abbreviation
	 */
	defineAbbreviation(abbreviation, definition) {
		if (this.#parent) {
			this.#parent.defineAbbreviation(abbreviation, definition);
			return;
		}
		this.#abbreviations[abbreviation] = definition;
		const regex = new RegExp("\\b(" + abbreviation + ")\\b", "ig");
		this.#abbreviationRegexes[abbreviation] = regex;
	}

	/**
	 * Defines content of a footnote.
	 * 
	 * @param {string} symbol - footnote symbol (e.g. "1")
	 * @param {MDBlock} footnote - content of the footnote
	 */
	defineFootnote(symbol, footnote) {
		if (this.#parent) {
			this.#parent.defineFootnote(symbol, footnote);
		} else {
			this.#footnotes[symbol] = footnote;
		}
	}

	/**
	 * @param {string} symbol
	 * @param {number} unique
	 */
	registerUniqueFootnote(symbol, unique) {
		if (this.#parent) {
			this.#parent.registerUniqueFootnote(symbol, unique);
		} else {
			var uniques = this.#footnoteInstances[symbol] || [];
			uniques.push(unique);
			this.#footnoteInstances[symbol] = uniques;
		}
	}

	/**
	 * Defines the URL for a given reference symbol.
	 *
	 * @param {string} symbol - reference symbol
	 * @param {string} url - URL
	 * @param {string|null} title - mouseover title attribute for links
	 */
	defineURL(symbol, url, title=null) {
		if (this.#parent) {
			this.#parent.defineURL(symbol, url, title);
		} else {
			this.#urlDefinitions[symbol.toLowerCase()] = url;
			if (title !== null) {
				this.#urlTitles[symbol.toLowerCase()] = title;
			}
		}
	}

	/**
	 * Tests if there are at least `minCount` lines available to read. If `p`
	 * is not provided it will be relative to `this.p`.
	 * 
	 * @param {number} minCount - minimum number of lines
	 * @param {number|null} p - line pointer
	 * @returns {boolean} whether at least the given number of lines is available
	 */
	hasLines(minCount, p=null) {
		let relativeTo = (p === null) ? this.p : p;
		return relativeTo + minCount <= this.lines.length;
	}

	/**
	 * Reads and returns an array of blocks from the current line pointer.
	 * 
	 * @returns {MDBlock[]} parsed blocks
	 */
	readBlocks() {
		var blocks = [];
		while (this.hasLines(1)) {
			let block = this.#readNextBlock();
			if (block) {
				blocks.push(block);
			} else {
				break;
			}
		}
		return blocks;
	}

	/**
	 * Creates a simple `MDInlineBlock` if no other registered blocks match.
	 * 
	 * @returns {MDInlineBlock|null} fallback block
	 */
	#readFallbackBlock() {
		if (this.p >= this.lines.length) return null;
		const lines = MDUtils.withoutTrailingBlankLines(this.lines.slice(this.p));
		if (lines.length == 0) return null;
		this.p = this.lines.length;
		return new MDInlineBlock(this.inlineMarkdownToSpans(lines.join("\n")));
	}

	/**
	 * Attempts to read one block from the current line pointer. The pointer
	 * will be positioned just after the end of the block.
	 *
	 * @param {MDState} state
	 * @returns {MDBlock}
	 */
	#readNextBlock() {
		while (this.hasLines(1) && this.lines[this.p].trim().length == 0) {
			this.p++;
		}
		if (!this.hasLines(1)) return null;
		for (const reader of this.blockReadersByPriority) {
			const block = reader.readBlock(this);
			if (block) return block;
		}
		const fallback = this.#readFallbackBlock();
		return fallback;
	}

	static #textWhitespaceRegex = /^(\s*)(?:(\S|\S.*\S)(\s*?))?$/; // 1=leading WS, 2=text, 3=trailing WS

	/**
	 * @param {string} line
	 * @returns {MDToken[]}
	 */
	#inlineMarkdownToTokens(line) {
		if (this.#parent) return this.#parent.#inlineMarkdownToTokens(line);

		var tokens = [];
		var text = '';
		var expectLiteral = false;

		/**
		 * Flushes accumulated content in `text` to `tokens`.
		 */
		const endText = function() {
			if (text.length == 0) return;
			const textGroups = MDState.#textWhitespaceRegex.exec(text);
			if (textGroups !== null) {
				if (textGroups[1].length > 0) {
					tokens.push(new MDToken(textGroups[1], MDTokenType.Whitespace, textGroups[1]));
				}
				if (textGroups[2] !== undefined && textGroups[2].length > 0) {
					tokens.push(new MDToken(textGroups[2], MDTokenType.Text, textGroups[2]));
				}
				if (textGroups[3] !== undefined && textGroups[3].length > 0) {
					tokens.push(new MDToken(textGroups[3], MDTokenType.Whitespace, textGroups[3]));
				}
			} else {
				tokens.push(new MDToken(text, MDTokenType.Text, text));
			}
			text = '';
		}

		for (var p = 0; p < line.length; p++) {
			const ch = line.substring(p, p + 1);
			const remainder = line.substring(p);
			if (expectLiteral) {
				text += ch;
				expectLiteral = false;
				continue;
			}
			if (ch == '\\') {
				expectLiteral = true;
				continue;
			}
			var found = false;
			for (const readerTuple of this.inlineReadersByTokenPriority) {
				/** @type {number} */
				const priority = readerTuple[0];
				/** @type {MDInlineReader} */
				const reader = readerTuple[1];
				const token = reader.readFirstToken(this, priority, remainder);
				if (token === null) continue;
				endText();
				tokens.push(token);
				p += token.original.length - 1;
				found = true;
				break;
			}
			if (!found) {
				text += ch;
			}
		}
		endText();
		return tokens;
	}

	/**
	 * Converts a line of markdown to an MDSpan.
	 * 
	 * @param {string|string[]} line
	 * @returns {MDSpan}
	 */
	inlineMarkdownToSpan(line) {
		let spans = this.inlineMarkdownToSpans(line);
		return (spans.length == 1) ? spans[0] : new MDMultiSpan(spans);
	}

	/**
	 * Converts a line of markdown to an array of MDSpan.
	 *
	 * @param {string|string[]} line
	 * @returns {MDSpan[]}
	 */
	inlineMarkdownToSpans(line) {
		var tokens = this.#inlineMarkdownToTokens((line instanceof Array) ? line.join('\n') : line);
		return this.tokensToSpans(tokens);
	}

	/**
	 * Converts a mixed array of `MDToken` and `MDSpan` elements into an array
	 * of only `MDSpan`.
	 * 
	 * @param {MDToken[]|MDSpan[]} tokens
	 * @returns {MDSpan[]}
	 */
	tokensToSpans(tokens) {
		var spans = tokens.slice();

		// Perform repeated substitutions, converting sequences of tokens into
		// spans, until no more substitutions can be made.
		var anyChanges = false;
		do {
			anyChanges = false;
			for (const readerTuple of this.inlineReadersBySubstitutePriority) {
				/** @type {number} */
				const priority = readerTuple[0];
				/** @type {MDInlineReader} */
				const reader = readerTuple[1];
				const changed = reader.substituteTokens(this, priority, spans);
				if (!changed) continue;
				anyChanges = true;
				break;
			}
		} while (anyChanges);

		// Convert any remaining tokens to spans, apply CSS modifiers.
		var lastSpan = null;
		spans = spans.map(function(span) {
			if (span instanceof MDToken) {
				if (span.type == MDTokenType.Modifier && lastSpan) {
					span.modifier.applyTo(lastSpan);
					lastSpan = null;
					return new MDTextSpan('');
				}
				lastSpan = null;
				return new MDTextSpan(span.original);
			} else if (span instanceof MDSpan) {
				lastSpan = (span instanceof MDTextSpan) ? null : span;
				return span;
			} else {
				throw new Error(`Unexpected span type ${span.constructor.name}`);
			}
		});

		return spans;
	}
}

class Markdown {
	/**
	 * Set of standard block readers.
	 * @type {MDBlockReader[]}
	 */
	static standardBlockReaders = [
		new MDUnderlinedHeaderBlockReader(10.0),
		new MDHashHeaderBlockReader(15.0),
		new MDBlockQuoteBlockReader(20.0),
		new MDHorizontalRuleBlockReader(25.0),
		new MDFencedCodeBlockReader(30.0),
		new MDIndentedCodeBlockReader(40.0),
		new MDOrderedListBlockReader(45.0),
		new MDUnorderedListBlockReader(50.0),
		new MDURLDefinitionBlockReader(95.0),
		new MDParagraphBlockReader(100.0),
	];

	/**
	 * All supported block readers.
	 * @type {MDBlockReader[]}
	 */
	static allBlockReaders = [
		...this.standardBlockReaders,
		new MDTableBlockReader(55.0),
		new MDDefinitionListBlockReader(60.0),
		new MDAbbreviationDefinitionBlockReader(90.0),
		new MDFootnoteDefinitionBlockReader(91.0),
	];

	/**
	 * Set of standard inline readers.
	 * @type {MDInlineReader[]}
	 */
	static standardInlineReaders = [
		new MDStrongInlineReader(10.0, [ 0.0, 2.0 ]),
		new MDEmphasisInlineReader(15.0, [ 5.0, 55.0 ]),
		new MDCodeInlineReader(20.0, [ 10.0, 60.0 ]),
		new MDImageInlineReader(25.0, 15.0),
		new MDLinkInlineReader(30.0, 20.0),
		new MDSimpleLinkInlineReader(35.0, 25.0),
		new MDHTMLTagInlineReader(80.0, 30.0),
	];

	/**
	 * All supported inline readers.
	 * @type {MDInlineReader[]}
	 */
	static allInlineReaders = [
		...this.standardInlineReaders,
		new MDStrikethroughInlineReader(21.0, [ 12.0, 50.0 ]),
		new MDFootnoteInlineReader(5.0, 40.0),
		new MDModifierInlineReader(90.0, 45.0),
	];

	/**
	 * Shared instance of a parser with standard syntax.
	 */
	static standardParser = new Markdown(this.standardBlockReaders, this.standardInlineReaders);

	/**
	 * Shared instance of a parser with all supported syntax.
	 */
	static completeParser = new Markdown(this.allBlockReaders, this.allInlineReaders);

	#blockReaders;
	#inlineReaders;

	#blockReadersByPriority;
	#inlineReadersByTokenPriority;
	#inlineReadersBySubstitutePriority;

	/**
	 * @param {MDBlockReader[]} blockReaders
	 * @param {MDInlineReader[]} inlineReaders
	 */
	constructor(blockReaders=Markdown.allBlockReaders, inlineReaders=Markdown.allInlineReaders) {
		this.#blockReaders = blockReaders;
		this.#inlineReaders = inlineReaders;

		this.#blockReadersByPriority = blockReaders.slice();
		this.#blockReadersByPriority.sort((a, b) => a.priority - b.priority);
		const duplicateAndSort = function(priorityFn) {
			var readers = [];
			for (const reader of inlineReaders) {
				const p = priorityFn(reader);
				const priorities = (p instanceof Array) ? p : [ p ];
				for (const priority of priorities) {
					readers.push([priority, reader]);
				}
			}
			readers.sort((a, b) => a[0] - b[0]);
			return readers;
		}			
		this.#inlineReadersByTokenPriority = duplicateAndSort((reader) => reader.tokenizePriority);
		this.#inlineReadersBySubstitutePriority = duplicateAndSort((reader) => reader.substitutePriority);
	}

	/**
	 * @param  {string} markdown
	 * @returns {string} HTML
	 */
	toHTML(markdown) {
		const lines = markdown.split(/(?:\n|\r|\r\n)/);
		const state = new MDState(lines);
		state.blockReadersByPriority = this.#blockReadersByPriority;
		state.inlineReadersByTokenPriority = this.#inlineReadersByTokenPriority;
		state.inlineReadersBySubstitutePriority = this.#inlineReadersBySubstitutePriority;
		const blocks = state.readBlocks();
		for (const reader of this.#blockReaders) {
			reader.postProcess(state, blocks);
		}
		for (const reader of this.#inlineReaders) {
			reader.postProcess(state, blocks);
		}
		return MDBlock.toHTML(blocks, state);
	}
}