- BOUNDA no Match "" at any boundary of a given type
- using ASCII rules
- NBOUND no Match "" at any word non-boundary using
- native charset rules for non-utf8, otherwise
- Unicode rules
- NBOUNDL no Match "" at any boundary of a given type
- using locale rules
- NBOUNDU no Match "" at any boundary of a given type
+ BOUNDA no Match "" at any boundary between \w\W or
+ \W\w, where \w is [_a-zA-Z0-9]
+ NBOUND no Like NBOUNDA for non-utf8, otherwise match
+ "" between any Unicode \w\w or \W\W
+ NBOUNDL no Like NBOUND/NBOUNDU, but \w and \W are
+ defined by current locale
+ NBOUNDU no Match "" at any non-boundary of a given type