The POSIX flag is passed to QScintilla for stardardisation of the regex
implementation. This only changes the syntax for sub-expressions. Before
this change it was '\( \)'. With the POSIX flag it is simply '( )' for
sub-expressions, consequently \( and \( have to be used for matching
parenthesis.
Both the Qt implementation (used in filters and REGEXP operator) and the
C++11 standard (possibly used in the future for the editor, if QScintilla
add support) use the the new syntax for sub-expressions.
References:
https://en.cppreference.com/w/cpp/regex/syntax_option_type
> If no grammar is chosen, ECMAScript is assumed to be selected.
https://en.cppreference.com/w/cpp/regex/ecmascript
> The Atom ( Disjunction ) is marked subexpression
Qt also uses subexpressions in the POSIX style.
http://doc.qt.io/qt-5/qregexp.html#capturing-parentheses
See issue #1625
58f52f13cb