Hi Frederic,
Right now, only section templates are supported. You can create a custom control using XBL, but this is more involved, isn't done from Form Builder, and is expected to be used to create "truly new" components that might require their own HTML, JavaScript, or CSS:
http://doc.orbeon.com/xforms/xbl/Also, I've created an RFE to capture this, and added a few ideas there:
https://github.com/orbeon/orbeon-forms/issues/2845Alex
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