-->
<!ELEMENT param (name, key, value?, type, hide?, option*)>
<!ELEMENT option (name, key, opt*)>
-<!ELEMENT sink (name, type, vlen?, nports?, optional?)>
-<!ELEMENT source (name, type, vlen?, nports?, optional?)>
+<!ELEMENT sink (name, key?, type, vlen?, nports?, optional?)>
+<!ELEMENT source (name, key?, type, vlen?, nports?, optional?)>
<!--
Bottom level elements.
Character data only.