I have not read the guideline for a long time, so did not have them in mind when answering.
But if I rember correct, there are a lot of bindings using the same syntax like in my answer…
Example from the Sonos Binding :
<channel-type id="currentalbumart">
<item-type>Image</item-type>
<label>Current Album Cover Art</label>
<description>Cover art of the album currently playing</description>
<state readOnly="true"/>
</channel-type>
<channel-type id="currentalbumarturl" advanced="true">
<item-type>String</item-type>
<label>Current Album Cover Art URL</label>
<description>Cover art URL of the album currently playing</description>
<state readOnly="true"/>
</channel-type>
<channel-type id="currenttrack" advanced="true">
<item-type>String</item-type>
<label>Current Track</label>
<description>Name of the current track or radio station currently playing</description>
<state readOnly="true"/>
</channel-type>
<channel-type id="currenttrackuri" advanced="true">
<item-type>String</item-type>
<label>Current Track URI</label>
<description>URI of the current track</description>
<state readOnly="true"/>
</channel-type>
<channel-type id="currenttransporturi" advanced="true">
<item-type>String</item-type>
<label>Current AV Transport URI</label>
<description>URI of the current AV transport</description>
<state readOnly="true"/>
</channel-type>