modify a small google maps project

I have a google maps application that allows the user to click on the map and create a multi-tab window. The user enters text into the different tabs. This application needs to be modified to allow a second user (user B, the “editor”) to edit the existing content placed in infowindow tabs by User A (the “writer”). B’s text should appear in a different colour to A’s. B must be able to delete parts of A’s text, add new text, and strikethrough parts of A’s text. There could be separate logins for User A and User B. Or it could be possible for Users A and B, after accessing the map in the same way, to adopt their different roles as writer and editor - e.g. by clicking on Editor or Writer buttons. Or there could be no login or buttons, and the person who creates the window is automatically the writer, and the next person who clicks on it has to be the editor. A database will be probably used to store content, although I will be open to an implementation that uses a text file. The existing code should be commented thoroughly and any additional code should also be commented.