Thread:Help talk:Notes on subobjects/Categorization and Display title for Subobjects (and for documentation pages in general)

Observing the subobject-related page-links listed in the "See also"" section at the bottom, i noticed that many belong to different categories:
 * Some belong to Category:Semantic MediaWiki documentation, like this page
 * Some are just Category:Documents.
 * Other are Category:User manual (& Document)

I'm wondering:
 * What should it be the "standard" categories for them?
 * Would it be ok to add another topic category Subobjects?
 * What should it be the parent of this new category? Would it be a diffuse or non-diffuse one? (its pages should also be listed n its parent?)

A generic remark in addition, some pages have display-title overrides and others not. Is there some rule about that?