How do I add multi-character replacements to prettify-symbols-alist?

[anton-trunov]

I'd like [** to be rendered as [△.

What would be the correct way of adding something like ("[**" . "[△") to prettify-symbols-alist? I don't want ** to be rendered as △ in all contexts.

[cpitclaudel]

It's tricky. There are multiple ways to do this:

• Use a font-lock rule with a display property (that is, don't use prettify-symbols-mode directly)
• Change the prettify-symbols-compose-predicate to only apply this prettification when preceded by a [
• Use a composition string. It's documented in the docstring of compose-region and reference-point-alist, which are a bit complex. The relevant part is this:

If it is a vector or list, it is a sequence of alternate characters and
composition rules, where (2N)th elements are characters and (2N+1)th
elements are composition rules to specify how to compose (2N+2)th
elements with previously composed N glyphs.

So you want this: (setq prettify-symbols-alist '(("[**" . (?\[ (Br . Bl) ?△)))). See https://emacs.stackexchange.com/questions/34808/using-prettify-symbols-with-strings-instead-of-characters

[anton-trunov]

Wow! It works. Thank you very much!

Do you think it is worth adding your example to README.md? For instance, to this section?

[cpitclaudel]

I think a brief link to this issue would be perfect, yes. Can you prepare a PR? :)