Regexp pattern allow \\cx sequence to specify control-x character.
Current implementation has two issues:

1) It allows x to be any character, including non-ASCII and non-printable ones;
For example, it is possible to have "\\c ", which will match "`".

2) It allows to construct a regexp that will match non-control characters;
For example "\\c`" will match " " (and the space char is not control-char).

Another thing that should also be reviewed is that x is currently case-sensitive.
For reference, perl treats \cA and \ca equally, and both regexps match ^A control-char.