A version of the category mapping for the site. Filters out data from the call to return only the category mappings for which the data has changed since the specified version. If not specified, all category mappings are returned. Typically, an application passes the version value of the last set of category mappings that the application stored locally. The latest version value is not necessarily greater than the previous value that was returned. Therefore, when comparing versions, only compare whether the value has changed.