In AUTOSAR_00048.xsd does a mmt.RestrictToStandards="AP" appinfo annotation indicate that this element is only valid for adaptive Autosar platform "description"?
The tag is primarily used to control the appearance of model elements in generated class diagrams and class tables that become part of the AUTOSAR specifications, e.g. „TPS Software Component Template“. For example, if a model element has a restriction to the AP, it will not appear in diagrams generated for the CP.
So, if a model element is not appearing in a specification in response to the tag, then this model element is not documented for the respective platform. And if there is no explicit documentation of this model element on the specific platform, then this fact could be taken as a hint that the model element is not relevant for the platform.
In general, the meaning of tags in the meta-model is explained in the AUTOSAR specification document TPS Generic Structure Template.