Counters are always generated content and cannot be selected.

third_party/WebKit/Source/core/layout/LayoutCounter.h

 /*
  * Copyright (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 50 matching lines @@
   static void DestroyCounterNode(LayoutObject&, const AtomicString& identifier);
   static void LayoutObjectSubtreeAttached(LayoutObject*);
   static void LayoutObjectSubtreeWillBeDetached(LayoutObject*);
   static void LayoutObjectStyleChanged(LayoutObject&,
                                        const ComputedStyle* old_style,
                                        const ComputedStyle& new_style);
 
   void UpdateCounter();
 
   const char* GetName() const override { return "LayoutCounter"; }
+  bool CanBeSelectionLeaf() const final { return false; }
 
  protected:
   void WillBeDestroyed() override;
 
  private:
   bool IsOfType(LayoutObjectType type) const override {
     return type == kLayoutObjectCounter || LayoutText::IsOfType(type);
   }
   PassRefPtr<StringImpl> OriginalText() const override;
 
@@ skipping 12 matching lines @@
 
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showCounterLayoutTree(const blink::LayoutObject*,
                            const char* counterName = nullptr);
 #endif
 
 #endif  // LayoutCounter_h