applyRule method
Applies heuristic rule to an operation on a document
and returns
resulting Delta.
Implementation
@override
Delta? applyRule(Delta document, int index, {int? len, Object? data, Attribute? attribute}) {
if (attribute == null || attribute.key != Attribute.style.key) {
return null;
}
assert(len == 1 && data == null);
final delta = Delta()
..retain(index)
..retain(1, attribute.toJson());
return delta;
}