Returns TRUE if tag is toggled on at exactly this point. If tag
is NULL, returns TRUE if any tag is toggled on at this point.
Note that if TextIter.beginsTag returns TRUE, it means that iter is
at the beginning of the tagged range, and that the
character at iter is inside the tagged range. In other
words, unlike TextIter.endsTag, if TextIter.beginsTag returns
TRUE, TextIter.hasTag will also return TRUE for the same
parameters.
Returns TRUE if tag is toggled on at exactly this point. If tag is NULL, returns TRUE if any tag is toggled on at this point.
Note that if TextIter.beginsTag returns TRUE, it means that iter is at the beginning of the tagged range, and that the character at iter is inside the tagged range. In other words, unlike TextIter.endsTag, if TextIter.beginsTag returns TRUE, TextIter.hasTag will also return TRUE for the same parameters.