In this recent post to his blog Ian Christian looks at how to use the sfForm component of the Symfony framework to create dynamic sub-forms without a refresh to build it.

wanted to create a form that allowed me to dynamically add sub-forms via JS, without round-trips to the server. I had a bit of a google, but failed to find much of use - so I wrote my own. This article contains my code for a proof of concept, and a brief description of what it does. It is proof of concept, and done as an example, so code isn't done perhaps as I might do in a real configuration, but I hope it provides help to others.

His end result lets you dynamically load in new form elements via some jQuery trickery. Complete code for the Javascript, view, form and the YAML markup for the model are included.