Add compose sequences for all four Serbo-Croatian accents on Latin and Cyrillic letters (the missing ones)
Serbo-Croatian uses either Latin or Cyrillic letters, and four marks when one needs to show the accent (in a dictionary mostly): double grave, inverted breve, grave, acute. No matter what the base language is (perhaps, English), it would be convenient to be able to input these letters when editing a dictionary entry for a Serbo-Croatian word.
I believe there is currently no deficiency of compose sequences for putting a grave or acute mark on a Latin or Cyrillic letter.
As for double grave, there are only sequences for Cyrillic letters, but no corresponding ones for Latin letters:
Multi_key grave grave Cyrillic_a | "а̏" # CYRILLIC SMALL LETTER A WITH COMBINING DOUBLE GRAVE ACCENT |
Multi_key grave grave Cyrillic_A
Multi_key grave grave Cyrillic_ie
Multi_key grave grave Cyrillic_IE
Multi_key grave grave Cyrillic_i
Multi_key grave grave Cyrillic_I
Multi_key grave grave Cyrillic_o
Multi_key grave grave Cyrillic_O
Multi_key grave grave Cyrillic_u
Multi_key grave grave Cyrillic_U
Multi_key grave grave Cyrillic_er
Multi_key grave grave Cyrillic_ER
(Maybe also additionally all the accent marks combined with Cyrillic_el and Latin L would be useful for some Serbo-Croatian dialects that retained the syllabic L in words like vlk "wolf", such as Timok-Prizren (Torlakian).)
I suggest adding similar sequences for Latin A, E, I, O, U, R (and maybe L, together with all the other accents on L).
As for inverted breve, there are no such sequences either for Cyrillic or Latin letters now. I suggest inventing a key that would act as an inverted breve after the Compose key and adding sequences with it (for the listed vocalic letters, including R and maybe L). Perhaps, the key could be parenright (since parenleft is sometimes used for breve, though not for all these vocalic letters--there, u or b are used).
I think that the comments and sequences in https://www.x.org/releases/current/doc/libX11/i18n/compose/sr_RS.UTF-8.html miss that R (Cyrillic_er) should be accentable, too. Example: cȓn / цр̑н "black". And maybe L (Cyrillic_el) in some dialects, which retain syllabic L (I mentioned this above); example: vlk "wolf".
And there, they implement the long falling accent as a circumflex, although as we can see in Wikipedia and other places, inverted breve is used for this. (Of course, if someone likes a circumflex, I don't think we should take away the possibility to do so, but we should also add the commonly used inverted breve to represent this accent. Well, I don't know, perhaps it'd be better to replace circumflex with inverted breve in these combinations for Serbian, since it's more correct, but I don't know what the actual wide-spread practice is, whether someone would prefer circumflex, and that would break the compatibility, but since this is limited just to Serbian, the compatibility problem might not be a real problem given that inverted breve is the correct mark.)