'exp' directive in included SPF record

In spf-draft-20040209.txt in the section 5.2 it says:

   Note: during recursion into an Include mechanism, explanations do not
   propagate out.

What does this exactly mean? Should 'exp' directives in included SPF records
be ignored?

Supposing following SPF records

xyz.com.     TXT  "v=spf1 include:inc.xyz.com exp=exp1.xyz.com -all"
inc.xyz.com  TXT  "v=spf1 a exp=exp2.xyz.com -all"

if the 'a' mechanism does not match, which one of the two explanations
should be taken?

Roger