Dear Maintainers,

  I propose to use the prefix argument in Interactive Highlighting.
  (the interactive function highlight-regexp)

  Without prefix all should stay identical.

  The numeric argument give the subexpression number of the regexp that 
is highlighted by font_lock or overlay.

  This allows to highlight

   - the 80th char of every line  C-u 1 M-s h r  and regexp ^.\{79\}\(.\)

   - the 6th column of a clean CSV file  C-u 1 M-s h r and regexp 
^\(?:[^,]*,\)\{5\}\([^,]*\),

   (clean CSV == with enough coma as you get multi-line matching with 
this regexp)

  I am not fluent with interactive stuff.
  I am not sure either how to treat errors.

  Have a nice day.
  Grégory Mounié


PS: Sorry for generating noise with my previous patch (BUG: 32362)