Where "extends" property is defined in JSON schema?

[Mingun]

Reference section on http://www.jsonschema2pojo.org/ describes, how extends keyword is translated to Java. There is also a mention of some part of the JSON schema specification(?):

Note: the extends rule in JSON schema accepts a schema or an array of schemas - jsonschema2pojo only supports the single schema variant.

But, according to the json-schema-org/json-schema-spec#348 (comment), JSON schema doesn't support inheritance and I can not find any mention of extends keyword on the official site

Where extends keyword is defined in JSON schema and what values it can have?

[joelittlejohn]

extends is a legacy keyword that existing in JSON Schema draft00/draft01/draft02/draft03 but was removed in draft04.

We can't easily support 'allOf' with Java's type system so a lot of people still prefer to use extends.