There is some initial support for commandblocks, but basically they don't work as you'd expect from Vanilla. For this reason, they need to be explicitly allowed in the configuration, they are disabled by default.
06-17-2017, 12:37 AM (This post was last modified: 06-17-2017, 12:37 AM by Mathias.)
The normal command block (id 137) works, but the GUI for editing its command doesn't work in 1.9-1.12 right now due to changes in Minecraft. It's quite useless though, since it can only run console commands at the moment.
Besides switching to 1.8, you can edit it by using plugins. I've attached an example plugin.