Some of the tools in adobe have a side panel when they are active. E.g. comments (screenshot below). Is it possible to create a custom panel for my plugin using the SDK?
I can't see anything in the SDK that gives access to that, the best you can do I think is to create your own palette, but it will not be able to be docked.
It is a major source of frustration for those of us trying to make the best user experience for our plug-ins: no, you can't. You can add tools, but not control the right hand panel. You can add sub-tools which appear in the second toolbar line, but without the same controls available to Adobe's.