When the format query parameter is XML or JSON, and data is being posted to the URL, validation occurs to ensure valid JSON or XML syntax, and to ensure the query conforms to the expected schema. This is achieved by using an XmlReader with a ValidationType of Schema. When validation fails, error will be returned as described in Errors.

When the format query parameter is HTML, all post data is passed directly to the HTML Player. The HTML Player is responsible for post data validation. The Player XML that is produced by the HTML Player is assumed to be valid.