New Feature: personal Commenting/Highlighting in Web pages

Hi! I have no clue if this is possible at all, but after all its a wish List, so here I go:


short description
My idea is a feature to add personal notes or comments on Web pages, similar to markups in MS Word, or commenting/highlighting Functions of .pdf viewers. Its kind of like editing the Web page, but the changes are saved locally, so whenever I open a Web page, the changes made by me previously to this specific page are loaded as well. A toggle button could determine whether I want to view the original Web page or the Web pages plus the changes I made. Maybe Its even possible to exchange the comment/markup/change/whatever-files between users.


Example
I am using some mathematical pages as reference for my studies. it would be cool if I could highlight the terms which i use most often. Some terms are for me easier to understand when I could add a little comment like "here the blabla-rule applies". or if I could add an Arrow to point from one calculation step to the next.
Theres a lot more examples, but i think (/hope) i already made the basic idea clear.



technical concept
I have only minimal knowledge in Web site publishing or browser technology, if any, but my idea is to save only the changes/enhancements made to the source code of a specific page on a users local drive, so it doesn't require too much space. If a page is loaded, Opera would check if any comments/changes exist on the local drive and, if yes, let the user decide whether to display the Original or the commented site.


I have no idea if this all makes sense at all, or is just a heap of bullsh. or even worse does already exist in any form, but i would certainly use this feature.

Greetz, Cyber

P.S. sorry this thread looks so crappy couldn't convince the Forum app to make line feeds.