I am working on an XML signing module and at least due to the timestamp I voted to go with the standard (XAdES) and implement it alike that.
I was able to digg into the list of Roles that someone might have.
However seems like there is no definition of role names in the standard?
The actual question that aririses to me is: Does any signed? subtree of XAdES support to add an arbitrary comment text? People want to just add some remark, when they sign. Did the standard forsee something?
I think you're correct, there's no definition of role names on the standard.
Regarding the "remark" you want to add, that seems like something application-specific. As such, I suggest using a ds:Object element, place your content in it, and also sign it. In xades4j you can do this using EnvelopedXmlObject.