You can either enable <literal class="html"> or develop your own custom tags.
From content.ini:
[literal]
AvailableClasses[]
# The class 'html' is disabled by default because it gives editors the
# possibility to insert html and javascript code in XML blocks.
# Don't enable the 'html' class unless you really trust all users who has
# privileges to edit objects containing XML blocks.
#AvailableClasses[]=html
CustomAttributes[]
