Here's a link on 'The Events "No data validation" option in XPages' that may go some way to answering your question..."How "No data validation" works in the JSF Lifecycle
The explanation for all of this requires an understanding of the JSF(Java Server Faces) lifecycle.
When the user submits a page to the server, the submission is processed in different phases, where in each phase it goes through all the controls and processes them.
When you submit a page, on the server it first restores the server-side control tree (Restore View phase), then it goes through all controls and copies the values from the browser form into each control's "submittedValue" field (Apply Request Values phase). Then it validates each control in the Process Validations phase, adding an error message to a list if not valid. Also if the field is configured as a non-string type, like Date, it'll convert it to a Date object, adding an error message to the list if there's a conversion problem. If the control is valid and converts OK, then the conversion will delete the value from the "submittedValue" field, and put the converted value into the control's "localValue". Then the phase will save the converted value into the underlying document field and remove the control's "localValue". Next the Invoke Application phase will process any actions associated with the event that submitted the page. Finally, if the action did not move to a different page, then the control tree is output as a HTML page that's returned to the browser (Render Response phase).
There are other explanations and diagrams of the JSF lifecycle on the web if you want to look into it more. "