stream is negotiated, e.g., through <xref target="RFC2327">SDP</xref>.
Since the media type defined for the isComposing status messages is
'application/im-iscomposing+xml', the SDP media line would contain
"application" as the media field of the "m" line and
"im-iscomposing+xml" as the "fmt" field, e.g.,
<figure><artwork><![CDATA[
  m=application 31467 tcp im-iscomposing+xml
]]></artwork></figure>
</t>