[ZPT] Extending tal:condition, making metal:define

[Evan Simpson]

From: "Guido van Rossum" <guido@digicool.com>
> > "if::" could also be "optional:", or whatever.
>
> OK, good.  Now I understand.  Should we do this for 1.1?  (It's not
> hard!)

From: <richard@bizarsoftware.com.au>
> Is there some reason why we couldn't just make use of 'exists'? It has no
> real use in the content/replace TAL operations. Make doNothing a false
> value. Or is that overloading the 'exists' keyword too much? And what's
the
> behaviour of the test in tal:replace? I think it'd be the same as
> replace/content - the tag stays as is, with no further processing.

I've put a proposal in the Project Wiki under DiscussTALES based on this
idea, using 'exists'.  I'd like to have it there for at least a day or two
before acting on it.  Please comment, especially on implementation details
like the singleton object used to signal non-existence.

Cheers,

Evan @ digicool