anchor.diff:  * `\n` matches the line feed character.
   * `\r` matches the carriage return character.
   * `\t` matches the tabulation character.
  -* `\v` matches the the vertical tabulation character.
  +* `\v` matches the vertical tabulation character.
   
   Character classes
   -----------------
  
positive.code: * `(?=...)` is a lookahead, it will match if its content matches the text
              following the current position
  * `(?!...)` is a negative lookahead, it will match if its content does
              not matches the text following the current position
  * `(?<=...)` is a lookbehind, it will match if its content matches
               the text preceding the current position
  * `(?<!...)` is a negative lookbehind, it will match if its content does
              not matches the text preceding the current position
  
  For performance reasons lookaround contents cannot be an arbitrary
  regular expression, it must be sequence of literals, character classes
  
negative.code:       character, or at the subject begin (except if specified that the
        subject begin is not a start of line).
  * `$` matches at the end of a line, that is just before a new line, or
        at the subject end (except if specified that the subject's end
        is not an end of line).
  * `\b` matches at a word boundary, when one of the previous character
         and current character is a word character, and the other is not.
  