SEP 5: Definition of breadcrumb navigation within metadata

Since 2022-06-01 posts using the default layout get automatic breadcrumb navigation of the form tag[0] / title. Where tag[0] is ‘journal’ they also receive non-hyperlinked date crumbs ie, JOURNAL / 2022 / 06 / 01 / Title for glanceable chronology.

At the same time support was added for a parent element, a la FOAF, so that the second element could be overridden when writing a series. This support should be expanded so that the whole hierarchy of breadcrumbs can be overridden at will.

The flexibility to only specify the leaf to be changed rather than detail the whole tree would be preferred, so long as it can be implemented in a robust way. Example: if the default behaviour (after ✅ SEP 4: Add taxonomical types alongside tags is implemented) is for the breadcrumb navigation to take the form type / tag[0] / title, then changing tag[0] should just be a case of navb: other_tag rather than the more verbose:

nava: type
navb: other_tag
navc: title

Though both forms should be supported.

Consideration should also be given to how many levels of depth the breadcrumb tree should support: arbitrary (infinite) or limited? Practically speaking, more than three layers would probably be visually confusing, stylistically unappealing, and represent a too deeply nested hierarchy. Still, there seems to be little reason for a limit to be strictly encoded except that it may improve build times by allowing less looping.