sensible-editor man page
sensible-editor, sensible-pager, sensible-browser — sensible editing, paging, and web browsing
sensible-editor, sensible-pager and sensible-browser make sensible decisions on which editor, pager, and web browser to call, respectively. Programs in Debian can use these scripts as their default editor, pager, or web browser or emulate their behavior.
Documentation of the EDITOR, VISUAL and PAGER variables in environ(7) and select-editor(1) for changing a user's default editor
Documentation of behavior of sensible-utils under a debian system is available under section 11.4 of debian-policy usually installed under /usr/share/doc/debian-policy (you might need to install debian-policy)