imports: Clarify when a document is "completely loaded"

spec/imports/index.html

@@ -406,8 +406,9 @@ <h3 id="fetching-import">Fetching Import</h3>
 <p>Every import that is not <a href="#dfn-import-link-async">marked as async</a> <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/the-end.html#delay-the-load-event">delays the load event in the Document</a>.
 
 <div class="informative">
-The <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#the-link-element"><code>link</code></a> element fires a simple event called <code>load</code>
-for successful loading attempt. For failed attempt, it fires a simple event named <code>error</code>.
+<p>The <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#the-link-element"><code>link</code></a> element fires a simple event called <code>load</code>
+for successful loading attempt. For failed attempt, it fires a simple event named <code>error</code>.</p>
+<p>As an import delays the load event, the <a href="http://dom.spec.whatwg.org/#document"><code>Document</code></a> isn't <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#completely-loaded">completely loaded</a> until loading attempts of all of its linked imports are finished.</p>
 </div>
 
 <h3 id="imports-and-csp">Imports and Content Security Policy</h3>