If you can select multiple notebooks it would be easy to move them and in conjunction with this #Feature Selecting multiple tags you a the perfect filtering machine.
For example with four clics you have all the notes from two notebooks that also have this tag and that one.
I hope you can understand me.
I will explain also how I understand the feature. It would be perfect if you can search using the tree (notebooks and tags) and also the search box.
For example right now if you click on a notebook/tag you are doing a new "search" and if you want to add something more in the search box everything is lost.
I think the best option is to have a new bar with the filters that are currently in use like in kibana. You can do it pushing control and the notebook/tag for example.
Thank you for the great job!