Validation

You can set up custom range and constraint validation rules using data-binding, that are continuously evaluated at runtime for any or all of the controls in a mobile or browser-based form.

Validation rules are set up by attaching a validation trait with one or more validator elements inside them to the control that needs to be validated. validator elements include a boolean value data-binding expression that references the validated control or any other control, and a validation error message. If the data-binding expression does not evaluate to true during the form fill session, validation fails, the error message is displayed next to the tested control, and the Submit button becomes disabled.

...
<textbox label='Required text'>
  <validation>
    <validator cond='{text != ""}'
      message= 'This field is required.'/>
  </validation>
</textbox>
...
The preset validation message is displayed next to the control when the validation condition isn't met

Figure 222. The preset validation message is displayed next to the control when the validation condition isn't met