\subsection{Class}
\label{sec:class}

The 'class' attribute describes the class of the tuple.  Multiple tuples
can have the same class name within a presence document. The naming of
classes is left to the presentity. The presentity can use this
information to group similar tuples or to convey information that the
presence agent can use for filtering.

\motivation{The class description is similar in spirit to the 'class'
attribute of XML elements, used to support Cascading Style Sheets.}  
