Puts the contents of the cursor into an action bar slot. If the action slot is empty and the cursor already holds an action, a spell, a companion (mount or non-combat pet), a macro, an equipment set, or an item (with a "Use:" effect), it is put into the action slot. If both the cursor and the slot hold an action (or any of the above data types), the contents of the cursor and the slot are exchanged.

Does nothing if the cursor is empty.