[0.8] Using one-way binding to propagate upward

[ragingwind]

An examples in Polymer primer, one-way binding for upward in Property change notification and Two-way binding is not working properly as much as I thought.

• With notify:true and readOnly:true: I couldn't change to 'prop' anyway.
• With notify:false and readOnly:true: I could change to 'prop' but never notify to host

<dom-module id="custom-elements">
  <template>
    <custom-element prop="{{value}}"></custom-element>
  </template>
</dom-module>

<script>
  Polymer({
    is: "custom-elements",

    properties: {
      value: {
        type: String,
        observer: 'valueChanged'
      }
    },

    valueChanged: function(newVal, oldVal) {
      console.log('Host value has been changed', newVal);
    }
  })

  Polymer({
    is: 'custom-element',

    properties: {
      prop: {
        type: String,
        notify: false,
        readOnly: true,
      }
    },

    ready: function() {
      this.prop = "from child";
      console.log(this.prop); // out "from child" if notify is false else out undefined
    }
  });
</script>

[ragingwind]

Sorry. answer is in the primer doc downward. I have to use _setProp