showdown/src/subParsers/codeBlocks.js

/**
 * Process Markdown `<pre><code>` blocks.
 */
showdown.subParser('codeBlocks', function (text, options, globals) {
  'use strict';

  /*
   text = text.replace(text,
   /(?:\n\n|^)
   (								// $1 = the code block -- one or more lines, starting with a space/tab
   (?:
   (?:[ ]{4}|\t)			// Lines must start with a tab or a tab-width of spaces - attacklab: g_tab_width
   .*\n+
   )+
   )
   (\n*[ ]{0,3}[^ \t\n]|(?=~0))	// attacklab: g_tab_width
   /g,function(){...});
   */

  // attacklab: sentinel workarounds for lack of \A and \Z, safari\khtml bug
  text += '~0';

  var pattern = /(?:\n\n|^)((?:(?:[ ]{4}|\t).*\n+)+)(\n*[ ]{0,3}[^ \t\n]|(?=~0))/g;
  text = text.replace(pattern, function (wholeMatch, m1, m2) {
    var codeblock = m1, nextChar = m2;

    codeblock = showdown.subParser('outdent')(codeblock);
    codeblock = showdown.subParser('encodeCode')(codeblock);
    codeblock = showdown.subParser('detab')(codeblock);
    codeblock = codeblock.replace(/^\n+/g, ''); // trim leading newlines
    codeblock = codeblock.replace(/\n+$/g, ''); // trim trailing whitespace

    codeblock = '<pre><code>' + codeblock + '\n</code></pre>';

    return showdown.subParser('hashBlock')(codeblock, options, globals) + nextChar;
  });

  // attacklab: strip sentinel
  text = text.replace(/~0/, '');

  return text;
});