Note RFC6570 and message body adjustment

Author: handrews

versions/3.0.4.md

@@ -3539,6 +3539,8 @@ Object | Condition
 
 Implementations of this specification MAY use an implementation of RFC6570 to perform variable expansion, however, some caveats apply.
 
+Note that when using `style: form` RFC6570 expansion to produce an `application/x-www-form-urlencoded` HTTP message body, it is necessary to remove the `?` prefix that is produced to satisfy the URI query string syntax.
+
 ### Equivalences Between Fields and RFC6570 Operators
 
 Certain field values translate to RFC6570 operators (or lack thereof):