Auto tagging from selected text

[seatrout]

I use a bookmarklet which would tag bookmarks automatically based on keywords in the selected text or description but bookmarklets of any sophistication are now broken. So I'd like to add that functionality here but I have no experience of Angular or of chrome extensions, so although I have a working routine to suggest tags from selected text I have no idea how to add it to this extension or how to call it.

Can anyone help: I need to pick up the selected text (which is presently put into the description field), read it, and then populate the tag field with suggestions.

What files should I be editing, and how can I trace the flow of control through the extension?