I find it would be useful to add a bit more explanation to this section.

1. define Letter and Char. I suspect
<Letter> ::= a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z
|A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z
<digit> ::= 1|2|3|4|5|6|7|8|9|0
<Char> ::= <Letter> | <digit> | (I don't know the appropriate notation to 
encompass NewLineChar etc)

Note that the usual use of <char> I found on the web was for <letter> | <digit>

2. expand on nl* and nl+
nl* ::= {nl} means 0 or more occurrences of nl
nl+ ::= nl {nl} means at least 1 occurrence followed by 0 or more
(note that I replaced {ws NewLineChar} by {nl} for nl+ to be consistent with 
nl* 

3. OBOChar
If I understand that one it is meant to provide a way to escape things? Based 
on the notation, an example of OBOChar would be (adding quotes to limit each 
example) "\A" or "\   1    &"
Would it be possible to add a few words on what is OBOChar and how it is to be 
used to make it clearer?