I would like to be able to replace a_e with aₑ using prettify symbols. However, if I add ("_e" . ₑ) to the prettify symbols alist, it will show the subscript e if _e is surrounded with spaces but not if a letter precedes the string as in the case of a_e.
How can I make the visual replacement even if the string is inside of a word ?
This can be done with prettify-symbols-compose-predicate but I do not understand a lot from the documentation of that symbol.
prettify-symbols-compose-predicate is set up by default to only
prettify symbols that are surrounded by non-symbol characters, which
is not your case. It gets passed the buffer positions at which the
symbol starts and ends, and the value which matched (which would be an
entry in prettify-symbols-alist). Since you don't care about those, you can do
(setq-local prettify-symbols-compose-predicate #'always)
which will ignore the arguments it's passed and return t.
