bug#32362: Interactive highlighting of sub-regexp

[Grégory Mounié]

 Dear maintainers,

 I propose to add to Interactive Highlighting (hi-lock.el) few lines in 
order to highlight only the first sub-regexps if it exists.

 The use case that interested me was to highlight the column of a CSV file.

 EG.:

 M-x highlight-regexp  then ^\(?:[^,]*,\)\{5\}\([^,]*\),.*$ for 
highlighting the 6th column of a clean CSV file

 I try to keep it as simple as possible as the function is in the 
documentation.

 The modified function has two paths: font-lock if enabled or directly 
overlay

 The sub-regexp detection is a bit rough for font-lock-mode case. I do 
not know how to do it perfectly without implementing a regexp engine or
using a much more complex detection regexp.
 For overlay-case, the code seems quite straightforward.

 Have a nice day,
 Grégory Mounié

0001-Interactive-Hightlighting-only-the-first-subexp-if-i.patch
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