Provides the same functionality as Vim's M command: place anchors on a web page and navigate between them.
Typing mk drops mark k where you currently are in the page. Later, typing 'k brings you back to where you were when you dropped the mark. k can be any letter from a to z.
The best way to use it is to load it as an unpacked extension from chrome (settings > load unpacked extension > select the 'extension' folder). This way it will work on any website, as long as it's activated.
That was the first step of development, but is still usable, if you have a local web server. This is not practical and not recommended.