is a variable defined in `
Its value is
The method for untabifying when deleting backward.
Can be `untabify' -- turn a tab to many spaces, then delete one space;
`hungry' -- delete all whitespace, both tabs and spaces;
`all' -- delete all whitespace, including tabs, spaces and newlines;
nil -- just delete one character.
You can customize this variable.
This variable was introduced, or its default value was changed, in
version 20.3 of Emacs.