Indentation of non-tagged lines relative to containing list.
This variable is used by the function `lisp-indent-tagbody' to indent normal
lines (lines without tags).
The indentation is relative to the indentation of the parenthesis enclosing
the special form. If the value is t, the body of tags will be indented
as a block at the same indentation as the first s-expression following
the tag. In this case, any forms before the first tag are indented by `lisp-body-indent'.