Which extension has search and tagging functionality?

Question

Google Chrome

I am looking for an example to do it myself, extensions for Chrome with the following functionality:
- find a string (word, url),
- mark the found string with a colored background,
- add a tooltip that opens with a mouseover and contains a clickable link.
I'm sure the functionality is not unique - can someone give a link to an example with such / similar functionality.
Alternatively, please describe the major milestones in the construction of such an extension, if possible with a few of Chrome's major features.