- XML comments are not skipped. Their delimiters are reduced or removed together with the surrounding spaces, their text is shown on the page.
- The <style> element is not implemented, as in many other readers (as well as the stylesheets). This is acceptable provided that the tags are correctly skipped; they are skipped (okay), but together with the surrounding spaces (which is wrong).
Here is an example. The source:
<?xml version="1.0" encoding="utf-8"?>
<FictionBook xmlns="http://www.gribuser.ru/xml/fictionbook/2.0" xmlns:l="http://www.w3.org/1999/xlink">
<description/>
<body>
<!--title>
<p><strong>La batalo de l’ vivo</strong></p>
</title-->
<section id="aS"><title><p>Preface</p></title>
<p>Foo <!--This is a comment--> Bar.</p>
<p>Plain <style name="s" xml:lang="en">Something very stylish</style> Plain.</p>
</section>
</body>
</FictionBook>
is rendered as

CoolReader renders it as expected:
S.P.
Here is an example. The source:
is rendered as
S.P.