doc: limit_except

[Gregg Reynolds]

On 3/16/07, Igor Sysoev <is at rambler-co.ru> wrote:

>
> The "!=" is good for me, thank you. I think the "==" should be omitted:
>
>      methods     POST ...
>      methods     LOCK UNLOCK ...
>      methods !=  GET ...

Ok by me.  Another option occurred to me, which might be clearer and
is certainly more powerful: use set operators.  Also, isn't the method
available in a variable?  So, e.g.

    $method memberof {POST...} { ... }
    $method not memberof {GET} {...}

Of course you could pick a different keyword (eltof, etc).  I would
avoid "in" to avoid a collision with the sense of "inwardly directed".
 You could do something like %member, too.

The nice thing about this is that it removes a directive and relies
only on syntax.  The directive name doesn't actually do any work,
after all. And with a set membership test you have a more general
capability.  Then it's just a predicate test, and you can support any
predicate you like:

   $UA memberof {IE SAFARI...} {...}

The semantics can be inferred directly from the syntax: no need for a directive.

Actually, now that I think about it, there is a good reason not to
omit the operator (whether if be equality or membership).  Something
like

    methods     LOCK UNLOCK ...

can easily be misread to mean "here is a list of methods against which
to test the request method."  But that would imply that

    methods != LOCK UNLOCK...

must mean "here's a list of methods _not_ to test the request method
against".  Logically this cannot imply that "methods" is everything
else.  The test is in fact a set membership test on the (one) request
method against the method-list args.  At least it looks that way to
me.  So both omission of an operator and use of the plural would be
misleading.

In any case, this will be an improvement on limit_except.  Now I can
write the documentation. ;)

gregg