Emacs defines certain column numbers to be @dfn{tab stops}. These
are used as stopping points by @key{TAB} when inserting whitespace in
Text mode and related modes (@pxref{Indentation}), and by commands
-like @kbd{M-i} (@pxref{Indentation Commands}). By default, tab stops
-are located every 8 columns. These positions are stored in the
-variable @code{tab-stop-list}, whose value is a list of column numbers
-in increasing order.
+like @kbd{M-i} (@pxref{Indentation Commands}). The variable
+@code{tab-stop-list} controls these positions. The default value
+is @code{nil}, which means a tab stop every 8 columns. The value
+can also be a list of column numbers (in increasing order) at which to
+place tab stops. Emacs extends the list forever by repeating the
+difference between the last and next-to-last elements.
@findex edit-tab-stops
@kindex C-c C-c @r{(Edit Tab Stops)}
@noindent
The first line contains a colon at each tab stop. The numbers on the
-next two lines are present just to indicate where the colons are. It
-is implicitly extended to infinity by repeating the last step.
+next two lines are present just to indicate where the colons are.
+If the value @code{tab-stop-list} is @code{nil}, as it is by default,
+no colons are displayed initially.
You can edit this buffer to specify different tab stops by placing
colons on the desired columns. The buffer uses Overwrite mode
-(@pxref{Minor Modes}). When you are done, type @kbd{C-c C-c} to make
+(@pxref{Minor Modes}). Remember that Emacs will extend the list of
+tab stops forever by repeating the difference between the last two
+explicit stops that you place. When you are done, type @kbd{C-c C-c} to make
the new tab stops take effect. Normally, the new tab stop settings
apply to all buffers. However, if you have made the
@code{tab-stop-list} variable local to the buffer where you called