Re: [prettify-symbols-mode] Two consecutive matches don't work?

[Eli Zaretskii <eliz@gnu.org>]

> Feedback-ID: ie15541ac:Fastmail
> Date: Wed, 18 May 2022 11:32:07 +0200
> From: Joost <joostkremers@fastmail.fm>
> 
> I'm dealing with some `.xml` files that contain data which uses the sequence `<<!` as some sort of operator. Because it's XML, the LESS-THAN sign needs to be encoded as `&lt;`, yielding `&lt;&lt;!`.
> 
> So I thought this would be the ideal use case for `prettify-symbols-mode`. I added `("&lt;" . ?<)` to `prettify-symbols-alist` and activated the mode.
> 
> Unfortunately, only the first `&lt;` in each sequence is prettified. This seems to be due to the fact that the second `&lt;` is followed by the exclamation mark: if I insert a space in between, prettification works.
> 
> Is there any way to remedy this?

prettify-symbols-mode is not general-purpose enough, its defaults are
tailored to prettifying keywords of programming languages, not just
any arbitrary strings of characters.

I think you will need to tailor prettify-symbols-default-compose-p or
roll your own predicate and bind prettify-symbols-compose-predicate to
that predicate, if you want to support such sequences.