SRFI 0 vs. R7RS cond-expand behavior incompatibility

[a2379]

SRFI 0 says that "the specification requires a macro-expansion time error to be signalled if a cond-expand form has no fulfilled clause".

However, R7RS-small says that "If none of the feature requirements evaluate to #t, then if there is an else clause, its expressions are included. Otherwise, the behavior of the cond-expand is unspecified."

Should we mark an implementation as supporting SRFI 0 if it does not throw an error? Some implementations like Chibi evaluate to #t if no clauses match.

On the other hand, I'm not sure if this is the right place to document compliance with the SRFI spec.