I don't know what extra functionality the recently-introduced explicit REST support brings to the table, but you can easily do REST web services by subclassing %CSP.Page and overriding the OnPage and OnPreHTTP methods....
Class MyRESTService Extends %CSP.Page
{
ClassMethod OnPage() As %Status [ ServerOnly = 1 ]
{
W "<html><title>web service</title>"
W "<div>"
W "message payload here"
W "</div></html>"
Q $$$OK
}
ClassMethod OnPreHTTP() As %Boolean [ ServerOnly = 1 ]
{
Do %response.SetHeader("Content-Type","text/html")
Q 1
}
}
Just set the content type to what your service responds with. E.g. if plain text instead of html just replace "text/plain" with "text/html" (and get rid of the html tags in the OnPage, just send your response string(s). Or if it is a JSON service, with "text/json".
As this is inheriting from %CSP.Page, the CSP gateway handles the request/response and you have access to any request parameters within the %request object, and you can also use the normal CSP session persistence mechanisms.