Slug

A short, lowercase name drawn from a list rather than invented: card-image, cartridge-reader, memcard-1, atari-2600, ps1-mc. The specifications use it wherever a field names a category everyone shares, so two producers writing about the same thing write the same string and a consumer can group by it.

A slug belongs to the specification that defines the field, or to the registry that field names. It is not a reverse-DNS name, which a producer mints for itself; the two grammars are disjoint, and which one a field takes is stated at the field.

This page is normative. When a specification says a field holds a slug, every rule here applies to that field.

Grammar

A slug is lowercase ASCII, at most 64 bytes, with runs separated by a single - and no leading or trailing one.

[a-z0-9]+(-[a-z0-9]+)*

A slug is exactly one DNS label, and a reverse-DNS name is two or more joined by ., so no string is both. A producer mints a reverse-DNS name without checking what a specification might assign later, and a specification assigns without auditing what producers have minted.

Who adds one

Every field that holds a slug says where its list lives, and there are only two answers.

• The specification owns it. The list grows with a new version of the spec.
• A registry owns it. The list grows by a PR against that registry, without a new version of the spec.

A producer does not invent a slug for a field that holds one. Inventing into a shared category does not extend it, it splits it: two producers naming one concept differently have given a consumer two unrelated strings to group by. A field that is a producer’s own to name says so, and takes a reverse-DNS name or free-form text instead.

An unfamiliar slug

Two rules cover every field that holds one.

• A consumer MUST round-trip a slug it does not recognise, unchanged. An unfamiliar name comes from a later version or a newer registry entry, and is never a reason to drop what it labels.
• A consumer MUST reject a value that is neither a well-formed slug nor a well-formed reverse-DNS name. That is not a name anybody could have written, so there is nothing to round-trip.
• Where a consumer cannot degrade gracefully, it MUST fail the operation rather than proceed on a guess. Preserving a name it does not understand is not licence to act as though it did.

What an unrecognised slug costs beyond grouping depends on the field, and the field says so. Most cost nothing: an unknown system or device_kind is a label a consumer carries and does not act on, and an unknown part kind is handled as aux. Some block an operation instead, and the field says which. An unknown card format blocks rebuilding the card, and an unknown role blocks matching a part to a socket; in both cases the consumer keeps the bundle whole and declines the write.

Slugs are compared whole and are opaque. The one exception is a numbered socket in the Save Roles registry, where a registered prefix covers every number; that registry states it, and nothing else in these specifications reads structure out of a slug.