Changed the bug summary from "categories : sub and related" to "Allow recursive categorization".

I mean, the category tag should be signed by a attribute which would express a type of relation:

• hyponymic relation (a sort of...)
• meronymic relation (a part of..., a member of...)
• attributing relation (by color, shape, size, ability or disability, nationality, technique, quality, awards etc.) including locative and timing categorization
• agentive and influence relation: (creator/work, device/product, company/product, discipline or profession/their subjects and terms, parent/children, subordination, owner/property, initiator/follower etc etc.)
• affiliation or modification: (affinity, derivation, former/newer identity etc.):

Category-view tools should allow to filter the content from subcategories according to the type of relation.