Meta model extension unparsable + new Symbols

  1. I wanted to extend the metamodel. When I use my plugin in the XML part, it says, that it is unparsable content.

unparsable content dsgvo:Informtionspflichtverletzung detected
line: 6
column: 7
nested error: unknown type dsgvo:Informtionspflichtverletzung [ warning ]

  1. I want new Symbols for my metamodel extension at Activities (together with possible task symbols) and message flows. The documentation did not helped very well.
    How could I manage this?

Thanks for the help