It would be a great deal, if it would be possible to tag all documents and (possibly) each position within each note with one or more tags. There should be a tag list for each shelf of notes, such that I can have different sets of tags for each shelf. It should then be possible to open the tag list for a shelf, click on a tag, and get a list of all usages of this tag with all documents and all locations within documents. Clicking on a usage should open the document (in case it is the tag of a whole document) or the document at the tagged position (if the tag is attached at a location within the document). The list of usages should be sorted according to the document names, and if there are more usages within a document, according to the page number. It should also be possible to jump from a tagged position within a note to the list of usages, and then to another usage, and so on.

To tag a note or a location within a note, one should be presented a list of available tags within this shelf. Then, one can select one or more tags, and possible also add one or more tags, which then can also be selected.

It would be ideal, if this approach was combined with folders (and subfolders ...) within each shelf, as is proposed in another feature request. One speciality of this request is, that these folders should be kept separately from shelves, in order that different tag groups can be maintained, one tag group for each shelf.

This feature, would make a great application, as GoodNotes already is, much more valuable. It would make GootNotes also a great knowledge management tool - with only little implementation effort. Looking forward for this feature being added! :-)