|| // /m line based ^$ $ str end (bfr \n)
.. ... /s . includes \n + one or more
?: /x ignore wh.space * zero or more
- = += -= *= etc /p preserve ? zero or one
+ = += last goto /p preserve ? zero or one
, => /a ASCII /aa safe {3,7} repeat in range
list ops /l locale /d dual | alternation
not /u Unicode [] character class