[DFDL-WG] clarifications needed for %ES; and %WSP*; entities

[Mike Beckerle]

Currently, we have gaps in the spec. E.g., in discussion of dfdl:initiator,
the spec says %ES; cannot appear alone in the list, but there is nothing
prohibiting one from just using
dfdl:initiator="%ES;%ES;" or dfdl:initiator="%ES: %ES;" to trivially work
around this constraint, even though both of these definitions are nonsense.

To avoid repeated discussion of this topic for each of initiator,
terminator, and separator, these statements need to be made where ES and
WSP* are defined, or in some other central location that discusses DFDL
String Literals and whitespace separated lists thereof.

%ES; can never appear as part of any other token. I.e., "%ES;A" is the same
as just "A" regardless of what "A" is. So %ES; can only appear as a
solitary token in a whitespace separated list of delimiter tokens or
nilValue tokens.

Furthermore, %ES; cannot be repeated in the list, since "%ES; %ES;" means
the same thing as just "%ES;".

%WSP*; similarly cannot be repeated in the list meaningfully, so that
should be prohibited as well.

(In fact repeating any token multiple times in the list can be prohibited.)

%WSP*; cannot be combined with %WSP+;, as the combination is equivalent to
just %WSP+; by itself. Furthermore %WSP*;%WSP*; means the same as %WSP*;
alone, so that should also be prohibited.

If we add these clarifications, then statements about how %ES; and %WSP*;
and their specific constraints for dfdl:initiator and dfdl:terminator and
dfdl:separator need not repeat these statements, and the constraints they
express do not have obvious gaps.

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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