Expansions

The _expand parameter allows you to specify additional data components that are not included by default to maximize API performance.
Parameter Description
_expand A list of attributes specifying additional data to return.
Individual expansions vary, and are documented for every resource. Expansion availability is further governed by:
  1. Role. Some expansions may be available, for example, only when the API is accessed with a private role.
  2. Result set size. Larger or resource intensive expansions can only be specified when a single item is retrieved (i.e. data retrieval by ID or when _limit=1).
Using the Accounts API as an example, passing the _expand=Settings parameter to /<API Version>/my/account will cause the Settings attribute to appear: 
{
    "D": {
        "Success": true,
        "Results": [
            {
                "Name": "Sample User",
                "Id": "20000426173054342350000000",
                "UserType": "Office",
                 /* Additional data omitted for brevity */
                "Settings": {
                    "SearchRestriction": {
                        "MlsStatus": [
                            "A",
                            "P"
                        ],
                        "PostalCode": null
                    }
                }
        ]
    }
}
Additionally, multiple expansions can be specified with a comma seperated list: 
  _expand=Photos,VirtualTours