code: function disableBackspaceIntoATable() {
          editor.on('keydown', function (e) {
            if (!isDefaultPrevented(e) && e.keyCode === BACKSPACE) {
              if (selection.isCollapsed() && selection.getRng(true).startOffset === 0) {
                var previousSibling = selection.getNode().previousSibling;
                if (previousSibling && previousSibling.nodeName && previousSibling.nodeName.toLowerCase() === "table") {
                  e.preventDefault();
                  return false;
                }
              }
            }
          });
        }
docs: Backspacing into a table behaves differently depending upon browser type.
  Therefore, disable Backspace when cursor immediately follows a table.