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Re: SV: SKiCal extensibility

At 14:44 08/09/2000 +0200, Greg FitzPatrick wrote:

(Please fold values to separate lines...) While this may appear OK at first
pass, it precludes any new values that are not expressly put in the ABNF.
The lesson from iCalendar would make the ABNF:

     qualstatparam = "QUALRULE" "=" *1("REQUIRED" / "NOTREQUIRED" /
                    "RECOMMENDED" / "NOTRECOMMENDED" / "PROHIBITED" /
                    "NOTPROHIBITED" / x-name / iana-token )

so that new values (or experimantal ones) can be added w/o breaking some
stricter interpretations!!

there's actually another way to do this, too....

if the original ABNF is

param = "FIRST" / "SECOND"

and you want to make it clear that you are extending a definition, you can
do it like this:

param =/ "THIRD"

which means that param can have all the old values, and THIRD too.
Section 3.3 of RFC 2234.

And of course, when you reuse something in a new context, you can always say:

paramv2 = param / "THIRD"

But in general, you want to include the iana-token thing unless you really, really want it to be a protocol error to specify an unknown value.

--
Harald Tveit Alvestrand, alvestrand@xxxxxxxxx
+47 41 44 29 94
Personal email: Harald@xxxxxxxxxxxxx