[web-animations-1] Disambiguate descendant

Author: birtles

web-animations-1/Overview.bs

@@ -205,6 +205,7 @@ urlPrefix: https://drafts.css-houdini.org/css-properties-values-api-1/; type: df
 spec:dom; type:interface; text:DocumentOrShadowRoot
 spec:dom; type:interface; text:EventTarget
 spec:dom; type:interface; text:Event
+spec:dom; type:dfn; text:descendant
 spec:dom; type:dfn; for:/; text:shadow root
 spec:css-color-4; type:value; text:transparent
 spec:css-fonts-4; type:property; text:font-weight