Support draft/2020-12 please

[kf6kjg]

{
    $schema: 'https://json-schema.org/draft/2020-12/schema',
    title: 'WIP',
    description: 'Placeholder.',
    type: 'object',
    additionalProperties: false,
    properties: {
        metadata: {
            $ref: '#/$defs/Metadata',
        },
    },
    $defs: {
        Metadata: {
            type: 'object',
            additionalProperties: false,
            properties: {

When fully fleshed out gives the warning The schema uses meta-schema features ($dynamicRef) that are not yet supported by the validator.