One place this is very useful is in business rules. See the section on templatized URls in business rules for more details. However anywhere that you can use templates in your form: labels, help, hint; display message, etc... the value can either come from the value in an actual form field or from _data values that are not in any way bound to the name of a control.
onInit and onSubmit are useful when you need to embed a
The embedding page and
must be in the the same domain/origin.Typically this means same uri scheme, host and port.