Hi, thank you for your question!

Yes, batch editing is supported!
On web client, select several tasks by pressing "shift",
priority: you can press shortcut key "P" setting the priority for these tasks;
context: you can drag these tasks to one of the contexts which are in the left column.

On Mac client,
priority: setting priority is in the same way as on web;
context: you can right-click the selected tasks, then choose a context.

Hope it helps,
Have a nice day !