I've been having a bit of a play around with it, and written a few small commands. The API documentation is really good, but this being early alpha software (currently v0.1.5) not everything works as expected.
For one of my commands I wanted to inject some HTML into the current webpage. Looking through the docs CmdUtils.injectHTML seemed to be exactly what I was after. Unfortunately it doesn't work, but the workaround is simple enough:
var html = 'content to inject'; var doc = CmdUtils.getDocument(); doc.body.innerHTML += html;
Hopefully this will be fixed in the next release.