Different $schema values in embedded resources

$schema is now definitively resource-scoped rather than document-scoped, as crossing a resource boundary is the same as following a $ref to an external resource.

Author: handrews

jsonschema-core.xml

@@ -635,7 +635,7 @@
  </t>
  <t>
  Note that some keywords, such as "$schema", apply to the lexical
- scope of the entire schema document, and therefore MUST only
+ scope of the entire schema resource, and therefore MUST only
  appear in a schema resource's root schema.
  </t>
  <t>
@@ -1167,37 +1167,19 @@
  media type "application/schema+json".
  </t>
  <t>
- The "$schema" keyword SHOULD be used in a resource root schema.
- It MUST NOT appear in resource subschemas. If absent from the root schema, the
- resulting behavior is implementation-defined.
+ The "$schema" keyword SHOULD be used in the document root schema object,
+ and MAY be used in the root schema objects of embedded schema resources.
+ It MUST NOT appear in subschemas. If absent from the document root schema,
+ the resulting behavior is implementation-defined.
  </t>
  <t>
- If multiple schema resources are present in a single document, then all
- schema resources SHOULD Have the same value for "$schema". The result of
- differing values for "$schema" within the same schema document is
- implementation-defined.
- <cref>
- Using multiple "$schema" keywords in the same document would imply that the
- feature set and therefore behavior can change within a document. This would
- necessitate resolving a number of implementation concerns that have not yet
- been clearly defined. So, while the pattern of using "$schema" only in root
- schemas is likely to remain the best practice for schema authoring,
- implementation behavior is subject to be revised or liberalized in
- future drafts.
- </cref>
- <cref>
- The exception made for embedded schema resources is to
- allow bundling multiple schema resources into a single schema document
- without needing to change their contents, as described later in this
- specification.
- </cref>
- <!--
- In particular, the process of validating an instance, including validating a
- schema as an instance against its meta-schema, only allows for a single set
- of rules across the entire instance document. There is no equivalent of
- changing the meta-schema partway through the validation for non-schema
- instances.
- -->
+ If multiple schema resources are present in a single document, then
+ schema resources which do not have a "$schema" keyword in their root
+ schema object inherit the meta-schema from the enclosing resource.
+ </t>
+ <t>
+ Embedded schema resources MAY specify different "$schema" values from their
+ enclosing resource, as any schema that can be referenced can also be embedded.
  </t>
  <t>
  Values for this property are defined elsewhere in this and other documents,
@@ -3769,6 +3751,11 @@ https://example.com/schemas/common#/$defs/count/minimum
  </t>
  <t>
  <list style="hanging">
+ <t hangText="draft-handrews-json-schema-03">
+ <list style="symbols">
+ <t>"$schema" MAY change for embedded resources</t>
+ </list>
+ </t>
  <t hangText="draft-handrews-json-schema-02">
  <list style="symbols">
  <t>Update to RFC 8259 for JSON specification</t>