Interface examples for handling "page notes" and highlighted text comments?

I'm working on a collections-based interface (think Pinterest or Dropbox), and we're implementing a feature that allows users to add Notes/Comments to various elements (folders/boards, files/pages, highlighted text, etc...).

These "notes" would be accessible either via an icon (say, a small Post-It note with the total count), or a sliding tray somewhere (there could be multiple notes for a specific item). Additionally, they'll need to access any notes they've added to specific text they've highlighted on a page. Should this be included in the standard Notes, or be treated differently? Not sure...

I'm having a hard time finding inspiration for this, and would love to see examples of Notes being handled really, really well.

Does anyone have any screenshots they could share of existing apps? Or any thoughts on how we should be handling this? I'm a bit stuck here and could use some inspiration :-)

Thank you so much!

-Lynn