When using the webservice to perform a lookup on any entity, the top level element in the response always represents that entity, except for when looking up iswcs.

For example:

http://musicbrainz.org/ws/2/artist/614e3804-7d34-41ba-857f-811bad7c2b7a :
<metadata><artist id="614e3804-7d34-41ba-857f-811bad7c2b7a">...</artist></metadata>

http://musicbrainz.org/ws/2/discid/TtCsoyi67uptOckJO7619MVqvDI- :
<metadata><disc id="TtCsoyi67uptOckJO7619MVqvDI-">...<release-list>...</release-list></metadata>

http://musicbrainz.org/ws/2/isrc/GBF087800019 :
<metadata><isrc id="GBF087800019"><recording-list>...</recording-list></isrc></metadata>

http://musicbrainz.org/ws/2/puid/0a7445c4-4bd4-3f07-c6db-8fd030a4dcdd :
<metadata><puid id="0a7445c4-4bd4-3f07-c6db-8fd030a4dcdd"><recording-list>...</recording-list></puid></metadata>

BUT:

http://musicbrainz.org/ws/2/iswc/T-010.067.890-7 :
<metadata><work-list>...</work-list></metadata>

I can't see any reason for this inconsistency. ISWCs are directly analogous to ISRCs, and therefore there behaviour should be identical too. Moreover, it precludes being able to ever return any information specific to the iswc rather than the works to which they are attached (c.f. sectors with discids).

A request for, e.g.:

http://musicbrainz.org/ws/2/iswc/T-010.067.890-7

should therefore return:

<metadata><iswc id="T-010.067.890-7"><work-list>...</work-list></iswc></metadata>