Very minor point that popped out when I was implementing a grammar parser for fun this evening. On page 49, the grammar for commenting out datums is written as
#; <atmosphere> <datum>
However, <atmosphere> contains <whitespace> which contains newlines, so that doesn't look correct.
#; (foo) <-- commented out by current grammar. Hmm...
If you still want to allow nested comments in the atmosphere portion there
#; #| first second |# (foo) <-- commented out
then maybe it needs a variant on <atmosphere> without newlines.