Prefix invisible inserts so they're distinguishable and tracked.

a11y_ prefix convention

Intent — A reserved naming prefix that marks tool-inserted, invisible-to-author artifacts (user-visible insertions keep ordinary names), so inserted content is distinguishable from authored content and a validator can cover it by prefix (our instance: the a11y_ prefix + InsertedContentValidator).

Motivation — the failure it kills

The tool inserts content: alt text, tags, off-canvas scaffolding. Mixing tool-inserted content with author-written content risks two failures: presenting invisible scaffolding as if the user wrote it, or an insert that isn't tracked and so isn't validated. The failure is untracked or mislabelled inserted content, and it recurs per inserter and per insertion site.

Why it's not just "name things sensibly" (or "keep a list of inserts")

Ad-hoc naming and a hand-maintained list are the two ways to fail here: neither is checkable, and the list drifts the moment an inserter forgets to append. The a11y_ prefix is a convention with a rule (invisible → a11y_, user-visible → not, spec-mandated → the spec name) that the inserted-content validator relies on, and every new inserter records itself with the registry so the validator covers it automatically. Naming by rule plus auto-registration is what makes the coverage mechanical rather than a promise. It is a repair-vocabulary constraint: it bounds how inserts are named and tracked, which makes validating them possible.

Mechanism

Invisible inserts are prefixed a11y_ (the invisible-insert prefix convention); user-visible inserts are not; spec-mandated names keep their spec name. New inserters call registry.Record(...), so the InsertedContentValidator automatically covers them; off-canvas placement uses dynamic geometry so it never bleeds on-page. Per-site corollaries live in the placement-audit doc.

Prerequisites

• The naming convention (the three-way rule) applied at every insertion site.
• A registry inserters record into, and a validator that reads it.

Consequences & costs

• Adherence is partly discipline. A mis-named or unregistered insert escapes coverage until caught.
• Spec-mandated names are exceptions to the prefix rule (by necessity), a small carve-out to track.
• Every inserter must call registry.Record — the auto-coverage only works if the registration habit holds.

Known uses

• The a11y_ prefix convention and its per-site corollaries.
• registry.Record(...) + the InsertedContentValidator (automatic coverage of registered inserts).

Related mechanisms

• Consumer — the InsertedContentValidator reads the registered inserts (naming + registration are what it depends on).
• See also (sibling) — remediation-verbs: both bound the remediator's move-space; this one bounds how inserted content is named and tracked.