tcl-tab-always-indent

tcl-tab-always-indent is a variable defined in `tcl.el'.
Its value is

t

Documentation:
Control effect of TAB key.
If t (the default), always indent current line.
If nil and point is not in the indentation area at the beginning of
the line, a TAB is inserted.
Other values cause the first possible action from the following list
to take place:

1. Move from beginning of line to correct indentation.
2. Delete an empty comment.
3. Move forward to start of comment, indenting if necessary.
4. Move forward to end of line, indenting if necessary.
5. Create an empty comment.
6. Move backward to start of comment, indenting if necessary.

You can customize this variable.