YouTrack 4.0 REST API - Update Issue?

You can use the "Apply command to an issue" method to perform any changes to the issue.
http://confluence.jetbrains.net/display/YTD4/Apply+Command+to+an+Issue

You can use REST method: POST /rest/issue/{issueById}?{summary}&{description}
But for some reason I can't find it in documentation. Filed JT-15971.

Thanks, but could you give me an example of how I would update the summary, description etc. as I can't seem to find an example in the documentation, and what I'm trying is failing:

rest/issue/ISSUE-9/execute?summary=KAYAK+SCENARIO%3a+New+design+item&description=ALM+KAYAK+SCENARIO%3a+1.1%0d%0a%0d%0aTest1&subsystem=Windows+Application

I've noticed my error:

rest/issue/ISSUE-9?summary=KAYAK+SCENARIO%3a+New+design+item&description=ALM+KAYAK+SCENARIO%3a+1.1%0d%0a%0d%0aTest1&subsystem=Windows+Application

Seems to work but the sub-system doesn't update, any ideas?

Problem that you can't do it in one request.
You need:
1. To update summary and/or description only:
rest/issue/ISSUE-9?summary=KAYAK+SCENARIO%3a+New+design+item&description=ALM+KAYAK+SCENARIO%3a+1.1%0d%0a%0d%0aTest1
2. To change all other issue fields use commands:
rest/issue/ISSUE-9/execute?command=subsystem+Windows+Application

Excellent - thanks very much that, it's all working now :-)