Merge pull request w3c#507 from jakearchibald/export-backdrop-root

Export backdrop root

Author: chrishtr

filter-effects-2/Overview.bs

@@ -112,7 +112,7 @@ See <a href="https://github.com/w3c/fxtf-drafts/issues/53">discussion in issue 5
 Note: No content that is a DOM ancestor of the Backdrop Root element should
 contribute to or affect the Backdrop Root Image.
 
-A <dfn>Backdrop Root</dfn> is formed, anywhere in the document, by an element in any of the following scenarios. See [[#BackdropRootTriggers]] for more details on each:
+A <dfn export>Backdrop Root</dfn> is formed, anywhere in the document, by an element in any of the following scenarios. See [[#BackdropRootTriggers]] for more details on each:
  * The root element of the document (HTML).
  * An element with a filter property other than "none".
  * An element with an opacity value less than 1.