src/subParsers/makemarkdown/txt.js
showdown.subParser('makeMarkdown.txt', function (node) {
'use strict';
var txt = node.nodeValue;
// multiple spaces are collapsed
txt = txt.replace(/ +/g, ' ');
// replace the custom ¨NBSP; with a space
txt = txt.replace(/¨NBSP;/g, ' ');
// ", <, > and & should replace escaped html entities
txt = showdown.helper.unescapeHTMLEntities(txt);
// escape markdown magic characters
// emphasis, strong and strikethrough - can appear everywhere
// we also escape pipe (|) because of tables
// and escape ` because of code blocks and spans
txt = txt.replace(/([*_~|`])/g, '\\$1');
// escape > because of blockquotes
txt = txt.replace(/^(\s*)>/g, '\\$1>');
// hash character, only troublesome at the beginning of a line because of headers
txt = txt.replace(/^#/gm, '\\#');
// horizontal rules
txt = txt.replace(/^(\s*)([-=]{3,})(\s*)$/, '$1\\$2$3');
// dot, because of ordered lists, only troublesome at the beginning of a line when preceded by an integer
txt = txt.replace(/^( {0,3}\d+)\./gm, '$1\\.');
// +, * and -, at the beginning of a line becomes a list, so we need to escape them also (asterisk was already escaped)
txt = txt.replace(/^( {0,3})([+-])/gm, '$1\\$2');
// images and links, ] followed by ( is problematic, so we escape it
txt = txt.replace(/]([\s]*)\(/g, '\\]$1\\(');
// reference URIs must also be escaped
txt = txt.replace(/^ {0,3}\[([\S \t]*?)]:/gm, '\\[$1]:');
return txt;
});