         }
 
         private func removeHeaderSynchronously(headerLevel: Int, spanning range: NSRange) {
-            guard let elementType = elementTypeForHeaderLevel(headerLevel) else {
+            guard let elementType = DOMString.elementTypeForHeaderLevel(headerLevel) else {
                 return
             }
             domEditor.unwrap(range: range, fromElementsNamed: elementType.equivalentNames)


        // MARK: - Header types

        private func elementTypeForHeaderLevel(_ headerLevel: Int) -> StandardElementType? {
            if headerLevel < 1 && headerLevel > DOMString.headerLevels.count {
                return nil
            }
            return DOMString.headerLevels[headerLevel - 1]
        }

        // MARK: - Raw HTML

        }

        func applyHeader(_ headerLevel:Int, spanning range:NSRange) {
            guard let elementType = DOMString.elementTypeForHeaderLevel(headerLevel) else {
                return
            }
            performAsyncUndoable { [weak self] in
