question: static private boolean isNoncapturingParen ( final String s , final int pos ) { final int len = s . length ( ) ; boolean isLookbehind = false ; if ( pos >= 0 && pos + 4 < len ) { final String pre = s . substring ( pos , pos + 4 ) ; isLookbehind = pre . equals ( "(?<=" ) || pre . equals ( "(?<!" ) ; } return pos >= 0 && pos + 2 < len && s . charAt ( pos + 1 ) == '?' && ( isLookbehind || s . charAt ( pos + 2 ) != '<' ) ; }
target:  Determines if the parenthesis at the specified position of a string is for a non-capturing group, which is one of the flag specifiers (e.g., (?s) or (?m) or (?:pattern). If the parenthesis is followed by "?", it must be a non- capturing group unless it's a named group (which begins with "?<"). Make sure not to confuse it with the lookbehind construct ("?<=" or "?<!").