code: function emptyEditorWhenDeleting() {
          function serializeRng(rng) {
            var body = dom.create("body");
            var contents = rng.cloneContents();
            body.appendChild(contents);
            return selection.serializer.serialize(body, { format: 'html' });
          }
  
          function allContentsSelected(rng) {
            if (!rng.setStart) {
              if (rng.item) {
                return false;
              }
  
              var bodyRng = rng.duplicate();
              bodyRng.moveToElementText(editor.getBody());
              return RangeUtils.compareRanges(rng, bodyRng);
            }
  
            var selection = serializeRng(rng);
  
            var allRng = dom.createRng();
            allRng.selectNode(editor.getBody());
  
            var allSelection = serializeRng(allRng);
            return selection === allSelection;
          }
  
          editor.on('keydown', function (e) {
            var keyCode = e.keyCode, isCollapsed, body;
  
            // Empty the editor if it's needed for example backspace at <p><b>|</b></p>
            if (!isDefaultPrevented(e) && (keyCode == DELETE || keyCode == BACKSPACE)) {
              isCollapsed = editor.selection.isCollapsed();
              body = editor.getBody();
  
              // Selection is collapsed but the editor isn't empty
              if (isCollapsed && !dom.isEmpty(body)) {
                return;
              }
  
              // Selection isn't collapsed but not all the contents is selected
              if (!isCollapsed && !allContentsSelected(editor.selection.getRng())) {
                return;
              }
  
              // Manually empty the editor
              e.preventDefault();
              editor.setContent('');
  
              if (body.firstChild && dom.isBlock(body.firstChild)) {
                editor.selection.setCursorLocation(body.firstChild, 0);
              } else {
                editor.selection.setCursorLocation(body, 0);
              }
  
              editor.nodeChanged();
            }
          });
        }
docs: Makes sure that the editor body becomes empty when backspace or delete is pressed in empty editors.
  
  For example:
  <p><b>|</b></p>
  
  Or:
  <h1>|</h1>
  
  Or:
  [<h1></h1>]