[draft-melnikov-sieve-external-lists] 2.2 Allow Extensions To Use List

[Robert Burrell Donkin <robertburrelldonkin@xxxxxxxxx>]

Proposal - Clarify Expected Behaviour For Unsupported Tests
===========================================================
Change
------
Require implementations to raise a compile time error when list
is used with an unsupported test.
Rationale
---------
Adopting a single clear rule on error handling increases interoperability.
Requiring a compile time error seems cleaner than alternatives such as
silently failing the test.

Proposal - Allow Extension Tests To Use Link
============================================
Change
------
Add explicit permission for implementations to support list for other
tests.
Rationale
---------
Extensions which find "list" useful should be encouraged to use it
as described.

Use Case: Mailing List Local Test
---------------------------------
if mailinglist :list "tag:example.org,2009-07-24:IEFT" {
   fileinto "standards";
}

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[1] Proposal
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2.2.  :list match type

   ABNF:

      MATCH-TYPE  =/ ":list"
           ; only valid for supported tests

   The new ":list" match type changes the interpretation of the "key-
   list" parameter to supported tests.  When the match type is ":list",
   the key-list becomes a list of names of externally stored lists.
   The external lists are queried, perhaps through a list-specific
   mechanism, and the test evaluates to "true" if any of the specified
   values matches any member of one or more of the lists.

   Implementations MUST support "address", "envelope" and "header" tests.
   Implementations MAY support other tests but MUST raise a compile
   time error when a script contains any standard test where support has
   not been explicitly specified.


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[2] Original Text
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2.2.  :list match type for "address", "envelope", and "header" tests

   ABNF:

      MATCH-TYPE  =/ ":list"
           ; only valid for "address", "envelope", and "header" tests

   The new ":list" match type changes the interpretation of the "key-
   list" parameter to the "address"/"envelope"/"header" test.  When the
   match type is ":list", the key-list becomes a list of names of
   externally stored lists.  The external lists are queried, perhaps
   through a list-specific mechanism, and the test evaluates to "true"
   if any of the specified values matches any member of one or more of
   the lists.