[css-contain-2] Fix bikeshed warning

css-contain-2/Overview.bs

@@ -1727,7 +1727,7 @@ Suppressing An Element's Contents Entirely: the 'content-visibility' property {#
  even if the element itself is still off-screen.
 
 
- * The element is <dfn>far away from the viewport</dfn>:
+ * The element is <dfn noexport>far away from the viewport</dfn>:
  In this state, the element's proximity to the viewport has been computed and is not [=close to the viewport=].
 
  * The element's [=proximity to the viewport=] is <dfn>not determined</dfn>: