Note it is a difference where you place modifiers such as "\c" in your expresion:

You can use the \c escape sequence anywhere in the pattern

Regardless from the accepted answers, which states that it is no difference of where to place modyfier in a regex pattern, its looks like it actually does matter.

example text:

asdasdasdasdasd wiktor asdasdasdasd   adasdasdasd wiktor asdasda ahjkjlkhjklasdasd asd asdasdasdasd iuuuu -       asdjkkkkkkkaopbsdasda                 wiktor ----(---------------------)--  

Match

\c^.*A?.*$
^\c.*A?.*$
^.*\cA?.*$
^.*A\c?.*$

will output:

No match

^.\c*A?.*$
^.*A?\c.*$
^.*A?.\c*$
^.*A?.*$\c

will output:

• vim -version VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Jun 1 2020 06:42:35)Included patches: 1-869