showdownjs/src/subParsers/encodeBackslashEscapes.js

/**
 * Returns the string, with after processing the following backslash escape sequences.
 *
 * attacklab: The polite way to do this is with the new escapeCharacters() function:
 *
 *    text = escapeCharacters(text,"\\",true);
 *    text = escapeCharacters(text,"`*_{}[]()>#+-.!",true);
 *
 * ...but we're sidestepping its use of the (slow) RegExp constructor
 * as an optimization for Firefox.  This function gets called a LOT.
 */
showdown.subParser('encodeBackslashEscapes', function (text) {
  'use strict';
  text = text.replace(/\\(\\)/g, showdown.helper.escapeCharactersCallback);
  text = text.replace(/\\([`*_{}\[\]()>#+-.!~])/g, showdown.helper.escapeCharactersCallback);
  return text;
});