XForms Validation / Binding Snippets

xforms-examples.xml

<!--
The constraint Property:
When evaluating to XPath false, the associated model item is not valid; 
the converse is not necessarily true. This model item property does not prevent 
form controls and XForms actions from setting invalid values into data nodes. 

Example:
Here, a constraint property associated with element my:to indicates 
that its value must be greater than that of element my:from.
-->
<instance>
  <my:range>
    <my:from />
    <my:to />
  </my:range>
</instance>
<bind nodeset="my:to" constraint=". > ../my:from" />

<!--
The calculate Property:
An XForms Model may include model items whose string values are computed from other values. 
For example, the sum over line items for quantity times unit price, or the amount of tax to 
be paid on an order. The formula for such a computed value can be expressed with a calculate 
property, whose XPath expression is evaluated, converted to a string with the XPath string() 
function, and stored as the value content of the calculated data node.

Example:
Here, we have associated a relevant property with element my:discount 
to indicate a discount of 10% is relevant when the order amount is greater than 1000.
-->
<instance>
  <my:order>
    <my:item>
      <my:amount />
      <my:discount />
    </my:item>
  </my:order>
</instance>
<bind nodeset="my:item/my:discount" calculate="../my:amount * 0.1"
      relevant="../my:amount > 1000"/>

<!--
The relevant Property:

Many forms have data entry sections that depend on other conditions. For example, a form
 might ask whether the respondent owns a car. It is only appropriate to ask for further 
information about their car if they have indicated that they own one.

Example:
Here, we have associated a relevant property with element my:discount 
to indicate a discount is relevant when the order amount is greater than 1000.
-->
<instance>
  <my:order>
    <my:item>
      <my:amount />
      <my:discount>100</my:discount>
    </my:item>
  </my:order>
</instance>
<bind nodeset="my:item/my:discount" readonly="true()"
      relevant="../my:amount > 1000"/>

http://www.w3.org/TR/2009/REC-xforms-20091020/#model-prop-calculate

http://stackoverflow.com/questions/6814240/how-do-i-populate-and-xforms-model-with-the-value-and-text-of-a-select1