JSON schema - variable contentMediaType - using regex?

Question

Is it possible to write a JSON schema that includes base64 encoded content where the media type could be anything? I presently have the following:

 "media" : { 
     "type": "object",
     "properties": {
         "content" : { 
             "type": "string", 
             "contentEncoding": "base64",
             "contentMediaType": "[a-z]\/[a-z]"
         }
      }
 },

Is this valid. Is it ok to use regex for the contentMediaType property?

If not, is the following valid?

 "media" : { 
     "type": "object",
     "properties": {
         "content" : { 
             "type": "string", 
             "contentEncoding": "base64",  
         },
         "contentMediaType": {
             "type": "string",
             "pattern": "[a-z]\/[a-z]"
          }
      }
 },

What would be the clearest way to achieve this?

Answer 1

This is what the spec says: https://json-schema.org/draft/2020-12/json-schema-validation.html#rfc.section.8.4

contentMediaType is a string. Your regex is a string, so it's interpreted literally. There is no matching media type in RFC 2046, so I would not expect things to go well. But your regex is so loose, why bother including it at all?

Do also keep in mind that JSON Schema interprets this keyword as an annotation only (https://json-schema.org/draft/2020-12/json-schema-validation.html#content) -- these properties are only present to provide information to the consuming application, and there will never be a time when evaluation of a data instance against this schema will fail against this keyword.