Add docs

hapi-fhir-base/src/main/java/ca/uhn/fhir/rest/param/ReferenceParam.java

@@ -200,6 +200,13 @@ public class ReferenceParam extends BaseParam /*implements IQueryParameterType*/
 		return myValue;
 	}
 
+	/**
+	 * Note that the parameter to this method <b>must</b> be a resource reference, e.g
+	 * <code>123</code> or <code>Patient/123</code> or <code>http://example.com/fhir/Patient/123</code>
+	 * or something like this. This is not appropriate for cases where a chain is being used and
+	 * the value is for a different type of parameter (e.g. a token). In that case, use one of the
+	 * setter constructors.
+	 */
 	public ReferenceParam setValue(String theValue) {
 		IdDt id = new IdDt(theValue);
 		String qualifier= null;