1) Because the term "fixnum" means something different in R6RS and R7RS-large, namely an exact integer whose smallest range is 24 bits and whose largest practical range is 63 bits at present, I think it should be avoided here. Rather, the term "ASCII codepoint", analogous to "Unicode codepoint" should be employed. This would be defined as an exact integer in the range 0 to 127 inclusive.

2) Remove all the repetitions of "char can be a fixnum or character object" and put it at the top: "Unless otherwise specified, char can be a fixnum or character object" once and for all.

3) The remaining uses of "fixnum" in the section on transformation procedures should be changed to "exact integer" or "exact non-negative integer" as appropriate. All other references shold be changed to "ASCII codepoint".

4) The sentence "The first ASCII standard was published in 1963" refers to a character encoding incompatible with today's ASCII. Leave it out or change it to "The present ASCII standard was first published in 1967."

5) Add predicates ascii-codepoint? and ascii-string?. The latter will be very valuable. ASCII strings should not be a disjoint datatype, but simply strings containing ASCII characters only.

6) Change the name of ascii-space-or-tab? to ascii-horizontal-whitespace?. This term is heavily used in RFCs.