collectAllStyles should return List<Style>

lib/src/models/documents/document.dart

@@ -127,7 +127,7 @@ class Document {
   }
 
   /// Returns all style for any character within the specified text range.
-  Style collectAllStyles(int index, int len) {
+  List<Style> collectAllStyles(int index, int len) {
     final res = queryChild(index);
     return (res.node as Line).collectAllStyles(res.offset, len);
   }

lib/src/models/documents/nodes/line.dart

@@ -370,32 +370,32 @@ class Line extends Container<Leaf?> {
   }
 
   /// Returns all style for any character within the specified text range.
-  Style collectAllStyles(int offset, int len) {
+  List<Style> collectAllStyles(int offset, int len) {
     final local = math.min(length - offset, len);
-    var result = Style();
+    final result = <Style>[];
 
     final data = queryChild(offset, true);
     var node = data.node as Leaf?;
     if (node != null) {
-      result = result.mergeAll(node.style);
+      result.add(node.style);
       var pos = node.length - data.offset;
       while (!node!.isLast && pos < local) {
         node = node.next as Leaf?;
-        result = result.mergeAll(node!.style);
+        result.add(node!.style);
         pos += node.length;
       }
     }
 
-    result = result.mergeAll(style);
+    result.add(style);
     if (parent is Block) {
       final block = parent as Block;
-      result = result.mergeAll(block.style);
+      result.add(block.style);
     }
 
     final remaining = len - local;
     if (remaining > 0) {
       final rest = nextLine!.collectAllStyles(0, remaining);
-      result = result.mergeAll(rest);
+      result.addAll(rest);
     }
 
     return result;

lib/src/widgets/controller.dart

@@ -64,10 +64,11 @@ class QuillController extends ChangeNotifier {
   }
 
   /// Returns all style for any character within the specified text range.
-  Style getAllSelectionStyles() {
-    return document
-        .collectAllStyles(selection.start, selection.end - selection.start)
-        .mergeAll(toggledStyle);
+  List<Style> getAllSelectionStyles() {
+    final styles = document.collectAllStyles(
+        selection.start, selection.end - selection.start)
+      ..add(toggledStyle);
+    return styles;
   }
 
   void undo() {

lib/src/widgets/toolbar/clear_format_button.dart

@@ -33,8 +33,13 @@ class _ClearFormatButtonState extends State<ClearFormatButton> {
         icon: Icon(widget.icon, size: widget.iconSize, color: iconColor),
         fillColor: fillColor,
         onPressed: () {
-          for (final k
-              in widget.controller.getAllSelectionStyles().attributes.values) {
+          final keys = <Attribute>{};
+          for (final style in widget.controller.getAllSelectionStyles()) {
+            for (final k in style.attributes.values) {
+              keys.add(k);
+            }
+          }
+          for (final k in keys) {
             widget.controller.formatSelection(Attribute.clone(k, null));
           }
         });