Support partial unhighlight selection

scripts/ui/question_player.gd

@@ -329,7 +329,7 @@ func _highlight_range(start: int, end: int) -> void:
 	if start == end:
 		return
 
-	if _remove_overlapping_highlights(highlights, start, end):
+	if _subtract_highlight_range(highlights, start, end):
 		_render_stem()
 		if stem_label.has_method("deselect"):
 			stem_label.deselect()
@@ -370,14 +370,21 @@ func _escape_bbcode(value: String) -> String:
 	return value.replace("[", "[lb]").replace("]", "[rb]")
 
 
-func _remove_overlapping_highlights(highlights: Array, start: int, end: int) -> bool:
-	var removed := false
+func _subtract_highlight_range(highlights: Array, start: int, end: int) -> bool:
+	var changed := false
 	for index in range(highlights.size() - 1, -1, -1):
 		var highlight_range: Dictionary = highlights[index]
-		if start < int(highlight_range.get("end", 0)) and end > int(highlight_range.get("start", 0)):
+		var highlight_start := int(highlight_range.get("start", 0))
+		var highlight_end := int(highlight_range.get("end", 0))
+		if start < highlight_end and end > highlight_start:
 			highlights.remove_at(index)
-			removed = true
-	return removed
+			if highlight_start < start:
+				highlights.insert(index, {"start": highlight_start, "end": start})
+				index += 1
+			if end < highlight_end:
+				highlights.insert(index, {"start": end, "end": highlight_end})
+			changed = true
+	return changed
 
 
 func _apply_saved_choice_state() -> void: