flyspell-highlight-incorrect-region

flyspell-highlight-incorrect-region is a compiled Lisp function in `flyspell.el'.

(flyspell-highlight-incorrect-region BEG END POSS)

Set up an overlay on a misspelled word, in the buffer from BEG to END.
POSS is usually a list of possible spelling/correction lists,
as returned by `ispell-parse-output'.
It can also be the symbol `doublon', in the case where the word
is itself incorrect, but suspiciously repeated.