knoppix@Microknoppix:~$ perl -E '
> $_ = qq{aabb\nwxy935TXB\n123};
> say $1 if m{(?x) ( a [^a] (?s) .* 9 (?-s) .* ) };'
abb
wxy935TXB
knoppix@Microknoppix:~$ 

##</code><code>##

m{(?i)Whole pattern case-insensitive}
m(Case-Sensitive(?i)case-insensitive(?-i)Case-Sensitive Again}
m{Case-Sensitive((?i)except in this capture)Case-Sensitive Again}
m{Case-Sensitive(?i:but not here)Case-Sensitive Again}
m{all case-insensitive(?-i:Except Here) and insensitive again}i
m{(?x) Use white-space\sfor readability(?-x)but literal spaces now};