The less than symbol (<) and ampersand (&) are two primary special characters to be concerned about. When including fields that may contain those characters you should use a special wrapper so the receiving system understands that they are data content and not part of the XML structure:
* *:: <span style="font-size: small;"><![CDATA[ '''''CONTENTS''''' ]]></span>*
For example, an address could contain ampersands, so it should be wrapped as follows: