Clarify: URL() can take object w/ URL stringifier (mdn#2768)

Fixes mdn#2767

files/en-us/web/api/url/url/index.html

@@ -27,8 +27,8 @@ <h3 id="Parameters">Parameters</h3>
 
 <dl>
 	<dt><code><var>url</var></code></dt>
-	<dd>A {{domxref("USVString")}} representing an absolute or relative URL. If
-		<code><var>url</var></code> is a relative URL, <code><var>base</var></code> is
+	<dd>A {{domxref("USVString")}} or any other object with a <a href="/en-US/docs/MDN/Contribute/Howto/Write_an_API_reference/Information_contained_in_a_WebIDL_file#stringifiers">stringifier</a> — including, for example, an {{htmlelement("a")}} or {{htmlelement("area")}} element — that represents an absolute or relative URL.
+		If <code><var>url</var></code> is a relative URL, <code><var>base</var></code> is
 		required, and will be used as the base URL. If <code><var>url</var></code> is an
 		absolute URL, a given <code><var>base</var></code> will be ignored.</dd>
 	<dt><code><var>base</var></code> {{optional_inline}}</dt>