e stripped.

Each tab is expanded with between 1 and `tab_width` spaces, so that the
next character's index becomes a multiple of `tab_width` (8 by default).

Parameters:

- `astring`: a multi-line string.
- `tab_width`: the number of columns between tab stops.
- `convert_whitespace`: convert form feeds and vertical tabs to spaces?
- `whitespace`: pattern object with the to-be-converted
  whitespace characters (default [\v\f]).
r