Invalid expressions such as ## and #123456789# (assuming that label has not been defined) signal an error even if *read-suppress* is true. The hyperspec says
#=
The #= notation is totally ignored. It does not read a following object. It produces no object, but is treated as whitespace[2].
Invalid expressions such as
##
and#123456789#
(assuming that label has not been defined) signal an error even if*read-suppress*
is true. The hyperspec saysFor example,
should not signal an error, but does.