You may not nest CDATA sections.
To write ]]> and you are not closing a CDATA section, the > must be written as >.
<xml_book>
<tags>
<appearance>
<![CDATA[
<animal>
<name language="Latin">T2</name>
<project>project1</project>
<weight>3 points</weight>
</animal>
]]>
</appearance>
</tags>
</xml_book>