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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/onSubmit

onInit and onSubmit are useful when you need to embed a  form in your own form and you want to programmatically submit the  form and initialize the form with your own documentThe onInit feature allows you to populate your embedded frevvo form with the data from your own HTML form. So if you want to pass some data from your web page to the frevvo form embedded into that same web page, you will use onInit. onInit function will execute when the frevvo form loads.

The onSubmit function allows you to copy the data from the frevvo form (when that frevvo form is submitted) into your HTML form. Then you can use your own JavaScript on your HTML page to process that data (for example save it somewhere else at your own convenience and time, etc.)

The embedding page and must be in the the same domain/origin.Typically this means same uri scheme, host and port.

The value of onInit must be an in scope javascript function. This onInit javascript function will be called before the form is instantiated. For example &onInit=getData will cause  to call the getData() javascript function. The onSubmit function will be called after the submit button is clicked.

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