Refer to collections of vocabularies as described by meta-schemas as dialects

[handrews]

A dialect is a collection of vocabularies plus a set of validation rules for that collection.

A meta-schema that uses $vocabulary describes a dialect, and is considered a "dialect meta-schema." https://json-schema.org/draft/2019-09/schema and https://json-schema.org/draft/2019-09/meta-schema` are dialect meta-schemas.

A meta-schema describing a dialect consisting of a single vocabulary and its standard syntax is considered to be a "vocabulary meta-schema" as well as being a "dialect meta-schema." https://json-schema.org/draft/2019-09/meta/validation and https://json-schema.org/draft/2019-09/meta/hyper-schema are vocabulary meta-schemas.

We should make this clear in the spec as the "dialect" terminology has proven helpful in discussions elsewhere.

[Relequestual]

Relevant:

I note that while we talk about how $schema represents an identifier for a "feature set", we don't define what that phrase actually means.

json-schema-spec/jsonschema-core.xml

Lines 1156 to 1158 in b615488

	The "$schema" keyword is both used as a JSON Schema feature set identifier and
	as the identifier of a resource which is itself a JSON Schema, which describes the
	set of valid schemas written for this particular feature set.

[Relequestual]

Also relevant

json-schema-spec/jsonschema-core.xml

Lines 2096 to 2097 in b615488

	Meta-schemas that do not use "$vocabulary" SHOULD be considered to
	require this vocabulary as if its URI were present with a value of true.

[handrews]

@Relequestual

I note that while we talk about how $schema represents an identifier for a "feature set", we don't define what that phrase actually means.

Yup, that's exactly what this is about! We should say "dialect" rather than "feature set", although the phrase "feature set" may be useful in explaining what a dialect is. But obviously it is not sufficient on its own to explain it.

I have a spreadsheet of dialect vs vocabulary and I have no idea why I didn't link it when I filed this.

https://docs.google.com/spreadsheets/d/18SIXnzyjXTJZgqeo5W-qIEwq-bNKXb5M76Pq_47r2Is/edit?usp=sharing

[Relequestual]

I expect this will be one of the later issues to get closed out when most others for the milestone are done.
Part of a final pass, if you like.