A frontmatter (note: Frontmatter) key (46 passages, no note) is declared neither by the type (note: Type) of the note (note: Note) nor among the common attributes (note: Attribute) of the profile (note: Profile). The value (35 passages, no note) is kept as written in the model (note: Model) and shown in the side panel (note: Side panel) of the page, but nothing interprets it: it produces no relation (note: Relation) and no typed (37 passages, no note) display. Most often a typo (4 passages, no note) in a key, or an attribute the project profile (9 passages, no note) has yet to declare.
Check (note: Check) W-ATTRIBUTE-UNKNOWN, severity (note: Severity) warning by default, documented with a before and after example in the check pages. The severity can be overridden per project (note: Project) or per repository (note: Knowledge repository).