I have moved the page to "OpenFOAM guide" in the new category "OpenFOAM source code documentation". This new category should be sufficiently broad to cover a wide range of (future) pages, but still specific enough as to only attract readers which are actually looking for this information.
Currently, the subpage "lagrangian" is a subpage of a parent page UML, and not linked via a category (as I understand is the convention?). I purposely made this a subpage ("OpenFOAM guide/UML/lagrangian"), since a future page "OpenFOAM guide/lagrangian" is not hard to imagine, whilst it will serve a different purpose. Linking it via a subpage (for the unicity in name) AND a category seems verbose to me.
Also, subpaging + categorizing (as is currently done for all "OpenFOAM guide/..." pages), has the problem that everything is categorized underneath the "O", which takes away a large part of the purpose of categorization.
Opinions?
Moving: Excellent
The convention is open to discussion
I think that having sub-pages as well as categories allows a page in the categories-section to assume two roles (show up in UML and "Physical models" if there was such a category for instance). Also (but I must check this) it is possible to have sub-categories to categories. But I'd only recommend that kind of sub-compartmentalization for categories with two-digit numbers of pages
