Prefilling form element values

• A data attribute on the form element points to an XML document containing the initial values:

  <form data="http://www.example.com/prefill/birddata.xml">
    <p><label>Quantity: <input type="number" name="quan"/></label></p>
    <p><label>Price: <input type="number" name="price"/></label></p>
  </form>

• Of course, the URL could point to a database-generated document that grabs the user's current values

• The external document is a well-formed formdata element:

  <formdata xmlns='http://n.whatwg.org/formdata'>
    <field name="quan">17</field>
    <field name="price">23.95</field>
    <!-- ... -->
  </formdata>

• MIME media type of the external document must be application/xml or some XML type.