The styling shared by every run overlapping [start, end): a concrete
value where the range agrees, MIXED where it doesn't. Keys no run
in range sets are absent (they inherit the node's TextStyle) — except
the additive flags, which read as false rather than undefined since a
run cannot un-set them. An empty range reads as {}. A reported fill
is the run's own object, not a copy — treat it as immutable.
The styling shared by every run overlapping
[start, end): a concrete value where the range agrees,MIXEDwhere it doesn't. Keys no run in range sets are absent (they inherit the node'sTextStyle) — except the additive flags, which read asfalserather thanundefinedsince a run cannot un-set them. An empty range reads as{}. A reportedfillis the run's own object, not a copy — treat it as immutable.