There is limited provision for regexp matching within Ido, enabled
through ido-enable-regexp (toggle with C-t). This allows
you to type ‘[ch]$’ for example and see all file names ending in
‘c’ or ‘h’.
If the value of this user option is non-nil, Ido will do regexp
matching. The value of this user option can be toggled within
ido-mode using ido-toggle-regexp.
Please note: Ido-style completion is inhibited when you enable regexp matching.