Exceptions while parsing markdown are caught and investigated and the minimal chunk of markdown is printed to console

js/markdown.js

 	 */
 	toHTML(markdown, elementIdPrefix='') {
 		const lines = markdown.split(/(?:\n|\r|\r\n)/);
+		try {
+			return this.#parse(lines, elementIdPrefix);
+		} catch (e) {
+			this.#investigateException(lines, elementIdPrefix);
+			throw e;
+		}
+	}
+
+	/**
+	 * @param {string[]} lines
+	 * @param {string} elementIdPrefix
+	 */
+	#parse(lines, elementIdPrefix) {
 		const state = new MDState(lines);
 		state.readersByBlockPriority = this.#readersByBlockPriority;
 		state.readersByTokenPriority = this.#readersByTokenPriority
 		}
 		return MDNode.toHTML(nodes, state);
 	}
+
+	/**
+	 * Keeps removing first and last lines of markdown to locate the source of
+	 * an exception.
+	 *
+	 * @param {string[]} lines
+	 * @param {string} elementIdPrefix
+	 */
+	#investigateException(lines, elementIdPrefix) {
+		var startIndex = 0;
+		var endIndex = lines.length;
+		// Keep stripping away first line until an exception stops being thrown
+		for (var i = 0; i < lines.length; i++) {
+			try {
+				this.#parse(lines.slice(i, endIndex), elementIdPrefix);
+				break;
+			} catch (e0) {
+				startIndex = i;
+			}
+		}
+		// Keep stripping away last line until an exception stops being thrown
+		for (var i = lines.length; i > startIndex; i--) {
+			try {
+				this.#parse(lines.slice(startIndex, i), elementIdPrefix);
+				break;
+			} catch (e0) {
+				endIndex = i;
+			}
+		}
+		const problematicMarkdown = lines.slice(startIndex, endIndex).join("\n");
+		console.error(`This portion of markdown caused an unexpected exception: ${problematicMarkdown}`);
+	}
 }

markdownjs.html

 
 * Unordered
 * Lists
-* Sub list
+    * Sub list
 
 1. Ordered
 2. Lists
-6. Sub list
+    6. Sub list
 
 A blockquote: