Anchor ::= 'anchorWordBoundary'
| 'anchorNonWordBoundary'
| 'anchorStartOfStringOnly'
| 'anchorEndOfStringOnlyNotNewline'
| 'anchorEndOfStringOnly'
| 'anchorPreviousMatchEnd'
| '$'
| ( 'lookahead' | 'negativeLookahead' | 'lookbehind' | 'negativeLookbehind'
)
Expression ')'