showdownjs/src/subParsers/hashHTMLBlocks.js

showdown.subParser('hashHTMLBlocks', function (text, options, globals) {
  'use strict';

  var blockTags = [
      'pre',
      'div',
      'h1',
      'h2',
      'h3',
      'h4',
      'h5',
      'h6',
      'blockquote',
      'table',
      'dl',
      'ol',
      'ul',
      'script',
      'noscript',
      'form',
      'fieldset',
      'iframe',
      'math',
      'style',
      'section',
      'header',
      'footer',
      'nav',
      'article',
      'aside',
      'address',
      'audio',
      'canvas',
      'figure',
      'hgroup',
      'output',
      'video',
      'p'
    ],
    repFunc = function (wholeMatch, match, left, right) {
      var txt = wholeMatch;
      // check if this html element is marked as markdown
      // if so, it's contents should be parsed as markdown
      if (left.search(/\bmarkdown\b/) !== -1) {
        txt = left + globals.converter.makeHtml(match) + right;
      }
      return '\n\n~K' + (globals.gHtmlBlocks.push(txt) - 1) + 'K\n\n';
    };

  for (var i = 0; i < blockTags.length; ++i) {
    text = showdown.helper.replaceRecursiveRegExp(text, repFunc, '^(?: |\\t){0,3}<' + blockTags[i] + '\\b[^>]*>', '</' + blockTags[i] + '>', 'gim');
  }

  // HR SPECIAL CASE
  text = text.replace(/(\n {0,3}(<(hr)\b([^<>])*?\/?>)[ \t]*(?=\n{2,}))/g,
    showdown.subParser('hashElement')(text, options, globals));

  // Special case for standalone HTML comments
  text = showdown.helper.replaceRecursiveRegExp(text, function (txt) {
    return '\n\n~K' + (globals.gHtmlBlocks.push(txt) - 1) + 'K\n\n';
  }, '^(?: |\\t){0,3}<!--', '-->', 'gm');

  // PHP and ASP-style processor instructions (<?...?> and <%...%>)
  text = text.replace(/(?:\n\n)([ ]{0,3}(?:<([?%])[^\r]*?\2>)[ \t]*(?=\n{2,}))/g,
    showdown.subParser('hashElement')(text, options, globals));

  return text;
});