gistfile1.txt

Content =
  all:(Element / Text)* {
  return all.join("").replace(/\n$/, '');
}
 
Element =
  startTag:StartTag content:Content endTag:EndTag {
    if (startTag != endTag) {
      throw new Error(
        "Expected </" + startTag + "> but </" + endTag + "> found."
      );
    }
 
    switch (startTag) {
      case 'em':
      case 'i':
        return '*'+content+'*';
      case 'b':
      case 'strong':
        return '**'+content+'**';
      case 'div':
      case 'p':
        return content+'\n';
      case 'sup':
      case 'sub':
        return '<' + startTag + '>' + content + '</' + endTag + '>';
      default:
        return content;
    }
  }
 
StartTag =
  "<" name:TagName ">" { return name; }
 
EndTag =
  "</" name:TagName ">" { return name; }
 
TagName = chars:[a-z]+ { return chars.join(""); }
Text    = chars:[^<]+  { return chars.join(""); }