Key legislation (for example, Article 91a II Basic Law, Article 109 III GG)
It tackles a matter not fully, but only in principle.
Unwritten legislative competences
Here it is assumed that the federation in some cases for legal matters has a legislative competence, even if this was not explicitly stated in the Basic Law. This is the case where legal matters for which the federation has the legislative competence could not regulated properly, without the regulation of another non-assigned matter, which is closely related to the assigned matter.
There is also the possibility that the federation regulates an assigned matter more profound because of the so-called Annex competence and thus expands its competence.
Last it is assumed, that the federation has a legislative competence, when a matter because of its nature could only be regulated by the federation.
Especially this last unwritten legislative competence is controversial and should therefore taken with caution.