Make sure to use UTF-8 as input encoding for all transferred data. Otherwise the chance for misinterpreted characters is given.

Nil Values Vs. Empty Values

Elements with NIL (or NULL) values must be provided with the nil attribute. Generally, elements with NIL values can be omitted in request bodies. In response bodies, such elements are added unless not specifically required.

Use CDATA Sections

Element values with reserved characters must be wrapped in cdata sections.