Converting between tab and space in Emacs

Emacs: "M-x untabify" will ConvertTabsToSpaces in the region; "M-x tabify" will ConvertSpacesToTabs.

Tab width

M-x set-variable  tab-width 7

For this session, force Emacs to indent with spaces, never with TABs:

M-x set-variable indent-tabs-mode nil

http://www.student.northpark.edu/pemente/emacs_tabs.htm