Adding MDLineBreakReader

js/markdown.js

 }
 
 /**
+ * Converts line breaks within blocks into line breaks in the HTML. Not
+ * included in any of the default reader sets since most flavors ignore
+ * line breaks within blocks.
+ */
+class MDLineBreakReader extends MDReader {
+	postProcess(state, blocks) {
+		MDNode.replaceNodes(state, blocks, (original) => {
+			if (!(original instanceof MDTextNode)) return null;
+			const lines = original.text.split("\n");
+			if (lines.length == 1) return null;
+			var nodes = [];
+			for (const [i, line] of lines.entries()) {
+				if (i > 0) {
+					nodes.push(new MDLineBreakNode());
+				}
+				nodes.push(new MDTextNode(line));
+			}
+			return new MDNode(nodes);
+		});
+	}
+}
+
+/**
  * Reads a verbatim HTML tag, and if it passes validation by `MDState.tagFilter`,
  * will be rendered in the final HTML document. Disallowed tags will be rendered
  * as plain text in the resulting document.

markdownjs.html

 		<script src="js/markdown.js"></script>
 		<script src="js/spreadsheet.js"></script>
 		<script>
-			var parser = new Markdown([ ...Markdown.allReaders, new MDSpreadsheetReader() ]);
+			var activeReaders = [];
+			var parser = null;
 			function onDocumentLoad() {
+				activeReaders = Markdown.standardReaders.slice();
+				parser = new Markdown(activeReaders);
 				document.getElementById('markdowninput').addEventListener('input', onMarkdownChange);
 				populateReaderCheckboxes();
 				setTimeout(onMarkdownChange, 0);
 				'Abbrevations': MDAbbreviationReader,
 				'HTML tags': MDHTMLTagReader,
 				'Modifiers': MDModifierReader,
+				'Line breaks': MDLineBreakReader,
 			};
-			var activeReaders = [];
 			function populateReaderCheckboxes() {
 				const container = document.getElementById('readercontainer');
 				var header = document.createElement('div');
 				container.append(blockContainer);
 				for (const name of Object.keys(blockReaderClasses).sort()) {
 					const readerClass = blockReaderClasses[name];
-					activeReaders.push(new readerClass());
 					const checkbox = makeReaderCheckbox(name, readerClass);
 					blockContainer.append(checkbox);
 				}
 				container.append(inlineContainer);
 				for (const name of Object.keys(inlineReaderClasses).sort()) {
 					const readerClass = inlineReaderClasses[name];
-					activeReaders.push(new readerClass());
 					const checkbox = makeReaderCheckbox(name, readerClass);
 					inlineContainer.append(checkbox);
 				}
 			}
 			function makeReaderCheckbox(name, readerClass) {
+				var isSelected = false;
+				for (const elem of activeReaders) {
+					if (elem.constructor === readerClass) {
+						isSelected = true;
+						break;
+					}
+				}
 				const check = document.createElement('input');
 				check.type = 'checkbox';
-				check.checked = true;
+				check.checked = isSelected;
 				check.addEventListener('change', () => {
 					handleCheckChanged(readerClass, check);
 				});
 
 A blockquote:
 
-&gt; "The only thing we have to fear is fear itself—nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance." - Franklin D. Roosevelt's First Inaugural Address
+&gt; "The only thing we have to fear is fear itself—nameless, unreasoning,
+&gt; unjustified terror which paralyzes needed efforts to convert retreat into
+&gt; advance." - Franklin D. Roosevelt's First Inaugural Address
 
 Some definitions:
 
 
 ## Inline Formats
 
-Normal, **double asterisk,** __double underscore,__ *asterisks,* _underscores,_ ~~double tildes,~~ ~single tildes,~ ^carets,^ ==double equals==, ``double backticks``, `single backticks`.
+Normal, **double asterisk,** __double underscore,__ *asterisks,* _underscores,_
+~~double tildes,~~ ~single tildes,~ ^carets,^ ==double equals==, ``double backticks``,
+`single backticks`.
 
-Lorem ipsum dolor sit amet,[^1] consectetur adipiscing elit.[^abc] Sed sodales in odio eget porta. Proin et erat sit amet erat semper mollis vitae ut turpis.[^foo] Ut ipsum dui, maximus sit amet suscipit at, dictum id nulla.[^bar] Aenean efficitur rhoncus nulla non fermentum.
+Lorem ipsum dolor sit amet,[^1] consectetur adipiscing elit.[^abc] Sed sodales
+in odio eget porta. Proin et erat sit amet erat semper mollis vitae ut
+turpis.[^foo] Ut ipsum dui, maximus sit amet suscipit at, dictum id nulla.[^bar]
+Aenean efficitur rhoncus nulla non fermentum.
 
 [^1]: Donec ut felis volutpat, gravida ipsum scelerisque, accumsan est.
 [^abc]: Cras dictum rutrum quam.
 [^foo]: Donec maximus bibendum lorem.
-[^bar]: Praesent consectetur tristique leo. Morbi nec nisi sit amet quam imperdiet vehicula eu feugiat tortor. 
+[^bar]: Praesent consectetur tristique leo. Morbi nec nisi sit amet quam
+ imperdiet vehicula eu feugiat tortor. 
 
 The HTML on the WWW is often full of JS and CSS.
 
 
 Click [here](#top) to return to the top. Referenced link to [Google][google].
 
-![alt text](https://picsum.photos/100/75) ![alt text](https://picsum.photos/101/75 "With a title") ![][testimage]
+![alt text](https://picsum.photos/100/75) ![alt text](https://picsum.photos/101/75 "With a title")
+![][testimage]
 
 [testimage]: https://picsum.photos/102/75
 [google]: https://google.com  "I prefer Duck Duck Go"
 
-Some verbatim &lt;span style="color:green;"&gt;HTML&lt;/span&gt;. A script tag will be ignored. &lt;script&gt;&lt;/script&gt;</textarea>
+Some verbatim &lt;span style="color:green;"&gt;HTML&lt;/span&gt;. A script tag
+will be ignored. &lt;script&gt;&lt;/script&gt;</textarea>
 		</div>
 		<div class="previewhalf half">
 			<div id="preview">