[css-ui] Tweak wording to recognize that iframes are replaced elements.

Author: fantasai

css-ui/Overview.bs

@@ -516,7 +516,7 @@ and if so, along which axis/axes.
 <tr><th>Value: </th><td>none | both | horizontal | vertical</td></tr>
 <tr><th>Initial:</th><td>none</td></tr>
 <tr><th>Applies to:</th><td>elements with 'overflow' other than visible,
-and optionally replaced elements representing images or videos, and iframes</td></tr>
+and optionally replaced elements such as images, videos, and iframes</td></tr>
 <tr><th>Inherited:</th><td>no</td></tr>
 <tr><th>Percentages:</th><td>N/A</td></tr>
 <tr><th>Media:</th><td>visual</td></tr>