<zk xmlns:w="client">

  <textbox id="Test" >

    <attribute w:name="doKeyPress_">

      function(evt){

           if (!this._shallIgnore(evt, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"))

              this.$doKeyPress_(evt);

      }

    </attribute>

  </textbox>

</zk>

​