code: func isWordByte(c int) bool {
  	return 'A' <= c && c <= 'Z' ||
  		'a' <= c && c <= 'z' ||
  		'0' <= c && c <= '9' ||
  		c == '_'
  }
docs: // isWordByte reports whether the byte c is a word character: ASCII only.
  // This is used to implement \b and \B.  This is not right for Unicode, but:
  //	- it's hard to get right in a byte-at-a-time matching world
  //	  (the DFA has only one-byte lookahead)
  //	- this crude approximation is the same one PCRE uses