CRM 2013: JavaScript – RetrieveMultiple records using FetchXML query and SOAP Endpoint

When retrieving information from multiple related records, I prefer using FetchXML and the SOAP endpoint over OData. To use FetchXML with JavaScript, we need the “RetrieveMultiple” message in the CRM Organization Service, which is available via what the CRM 2013 SDK (version 6.0.2 at time of writing) calls the “Modern App SOAP endpoint”.