Dynamic defaults for Semantic Forms

Summary
With a bit of Javascript and some additions to your form definitions you can set the content of form fields to any value you like, constant or generated. This even works, when the field is pre-filled.

Problem
Presently you can set defaults for form fields only to constant values (with some exceptions, granted). It is not possible to set the defaults to dynamic data, e.g. results from template calls or from. If there is preloaded data, you can not force it to default values, at all.

What do you have to do?

 * 1) Copy the javascript code from User:F.trott/dynamicSFDefaults.js to somewhere where it is executed, e.g. the MediaWiki:Common.js page of your wiki
 * 2) In your form definition, include some of the following: