Opening block tags should have no whitespace immediately following them other than line breaks (and indentation on the following line).

<!-- NOT ALLOWED -->
<sect1>WHITESPACE
</sect1>

Opening inline tags should have no whitespace immediately following them.

<!-- NOT ALLOWED -->
This is the class <classname> Zend_Class</classname>.

<!-- OK -->
This is the class <classname>Zend_Class</classname>.

Closing block tags may be preceded by whitespace equivalent to the current indentation level, but no more than that amount.

<!-- NOT ALLOWED -->
    <sect1>
     </sect1>

<!-- OK -->
    <sect1>
    </sect1>

Closing inline tags must not be preceded by any whitespace.

<!-- NOT ALLOWED -->
This is the class <classname>Zend_Class </classname>

<!-- OK -->
This is the class <classname>Zend_Class</classname>

Multiple line breaks within or between tags are not allowed.

<!-- NOT ALLOWED -->
<para>
    Some text...

    ... and more text
</para>


<para>
    Another paragraph.
</para>

<!-- OK -->
<para>
    Some text...
    ... and more text
</para>

<para>
    Another paragraph.
</para>

Tags at the same level must be separated by an empty line to improve readability.

<!-- NOT ALLOWED -->
<para>
    Some text...
</para>
<para>
    More text...
</para>

<!-- OK -->
<para>
    Some text...
</para>

<para>
    More text...
</para>

The first child tag should open directly below its parent, with no empty line between them; the last child tag should close directly before the closing tag of its parent.

<!-- NOT ALLOWED -->
<sect1>

    <sect2>
    </sect2>

    <sect2>
    </sect2>

    <sect2>
    </sect2>

</sect1>

<!-- OK -->
<sect1>
    <sect2>
    </sect2>

    <sect2>
    </sect2>

    <sect2>
    </sect2>
</sect1>