config::Schema

Every declaration of one app or library.

Detailed description

A schema is an id, a title, its levels, the ordered category list and the ordered rows. It is not a singleton: each app or library owns one, and one app model can show several (config-ui §CFGM-2, §CFGV-1).

add() checks each declaration as it arrives. A declaration that is not valid is kept, so a lookup does not silently miss, and errors() names the defect. `testConfigSchema` holds each rule.