+Syntax could vary greatly here, both for the [[PreprocessorDirective]] and
+for the condition itself.
+
+> I think this is a good thing to consider, although conditionals tend to
+> make everything a lot more complicated, so I also want to KISS, and not
+> use too many of them.
+>
+> I'd probably implement this using the same method as pagespecs, so 'and',
+> 'or', '!', and paren groupings work.
+>
+> It could be thought of as simply testing to see if a pagespec matches
+> anything, using a slightly expanded syntax for the pagespec, which would
+> also allow testing for things like link(somepage),
+> created_before(somepage), etc.
+>
+> That also gives us your "any pagespec" for free: "page or page or page".
+> And for "all pagespec", you can do "page and page and page".
+>
+> For plugins testing, maybe just use "enabled(name)"?
+>
+> I'm not sure what the use cases are for thispage, sourcepage, and
+> included. I don't know if the included test is even doable. I'd be
+> inclined to not bother with these three unless there are use cases I'm
+> not seeing.
+>
+> As to the syntax, to fit it into standard preprocessor syntax, it would
+> need to look something like this:
+>
+> \[[if test="enabled(smiley)" """foo"""]]
+>
+> --[[Joey]]
+
+>> [[PageSpec]] syntax seems perfect, and your proposed syntax for the `if`
+>> [[PreprocessorDirective]] looks fine to me.
+>>
+>> [[PageSpec]]s don't give you `none` for free, since `!foo/*` as a boolean
+>> would mean "does any page not matching `foo/*` exist", not "does `foo/*`
+>> match nothing"; however, I don't really care much about `none`, since I
+>> just threw it in while brainstorming, and I don't know any compelling use
+>> cases for it.
+>>
+>> `enabled(pluginname)` will work perfectly, and `!enabled(pluginname)`
+>> makes `disabled` unnecessary.
+>>
+>> A few use cases for `included`, which I would really like to see:
+>>
+>> * On the sidebar page, you could say something like \[[if test="!included"
+>> """This page, without this help message, appears as a sidebar on all
+>> pages."""]]. The help text would then only appear on the sidebar page
+>> itself, not the sidebar included on all pages.
+>>
+>> * On [[blog]] entries, you could use `included` to implement a cut.
+>> (Please don't take that as an argument against. :) ) For instance, you
+>> could use included rather than [[plugins/toggle]] for the detailed
+>> changelogs of ikiwiki, or to embed an image as a link in the feed rather
+>> than an embedded image.
+>>
+>> Some use cases for `thispage`:
+>>
+>> * You could use `thispage` to include or exclude parts of the sidebar based
+>> on the page you include it in. You can already use subpages/sidebar for
+>> subpages/*, but `thispage` seems more flexible, makes it trivial to have
+>> common portions rather than using [[plugins/inline]] with the `raw`
+>> option, and keeps the sidebar in one place.
+>>
+>> * You could use `thispage` to implement multiple different feeds for the
+>> same content with slightly different presentation. For instance, using
+>> templates for image inclusion, you could offer a feed with image links
+>> and a feed with embedded images. Similarly, using templates for cuts, you
+>> could offer a feed with cuts and a feed with full content in every post.
+>>
+>> I don't have any particular attachment to `sourcepage`. It only makes
+>> sense as part of a template, since otherwise you know the source page when
+>> typing in the if.
+>>
+>> --[[JoshTriplett]]
+
+This is now completely [[todo/done]]! See [[plugins/conditional]].
+
+--[[Joey]]
+
+> You rock mightily. --[[JoshTriplett]]
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