It would be nice if the web service supported the submission of iswcs. Given that recording<=>isrc is equivalent to work<=>iswc, the syntax should be equivalent to that used for the submission of isrcs, for example:

POST http://test.musicbrainz.org/ws/2/work?client=WebService-MusicBrainz-NGS-TestSuite-0.01
Content-Type: application/xml; charset=utf-8

<?xml version="1.0" encoding="UTF-8"?>
<metadata xmlns="http://musicbrainz.org/ns/mmd-2.0#"><work-list><work id="257d563b-976e-3893-ae57-b0ba6e77971a"><iswc-list count="1"><iswc id="T-010.067.890-7"/></iswc-list></work></work-list></metadata>