The Open Commerce API currently supports two data formats for resources: JSON and XML. JSON is the default format, but you can explicitly specify XML.
How you specify a format depends on the underlying HTTP method. For GET
requests, you provide a value for the URL request parameter
format (valid values are json and xml). For POST, PUT,
and PATCH requests, you provide a value for the HTTP header
content-type (valid values are application/json,
application/xml, and text/xml). The HTTP header
content-type has precedence over the URL request
parameter format.