olemus
kirjamärki täiendav modifitseeriv lisamärgis,
tähistab foneetilist vastet, mis erineb algse märgi omast
=
a sign, which when added to a letter indicates a difference in pronunciation from the same letter when unmarked or differently marked; diacritics may appear above or below a letter or in some other position such as within the letter or between two letters

ülevaateid
https://en.wikipedia.org/wiki/Diacritic

http://diacritics.typo.cz/

http://unicode.org/charts/PDF/U0300.pdf

mõned sagedamad