I think a better case of ambiguity is:

{{{
How about //a link, like http://example.org, in italic text? //
}}}

--

I think it gets more complex when the protocol isn't recognised by the wiki parser. 
If a wiki that limits the procotols for raw links, to say just (http, ftp). What should a parser do with {{{ https://www.example.org }}} ? 

I think it should render it as seen ({{{ http://www.example.org }}}) and not treat the // as italics.

-- JaredWilliams, 2007-02-23

Url (plus e-mail address) is something like 
{{{
(\b[a-z]{3,6}://\S+[^,.;:?!'"() ](\s|[,.;:?!'"()]|$)|[A-Za-z._-]+@[a-z.-]+[a-z]) 
}}}
matched before the the italics are matched.  The example given before:
{{{
... for example://apples//, oranges, **pears** ...
}}}

is an example of when markup adds perceived spacing that doesn't appear in the rendered page -- and as such is an obvious mistake on the side of the user. Of course, it would be nice to minimize the opportunities for such errors -- MoinMoin does have a list of accepted protocols and uses only these -- also for security reasons. Limiting the length of the protocol name is another trick -- unfortunately, from the kind of "smart" ones that work only sometimes and add to the confusion. 

Personally I can live both without highlighting urls or with an apportunity for occasional wrong highlighting. I can also live with "{{{__foo__}}}" for italics, but we discussed this already.
-- RadomirDopieralski, 2007-02-23

I think the following line is in error and that italics there should not be parsed, but rather shown as double slash:

{{{
This is what can go wrong://this should be an italic text//.
}}}

In a sentence, if you use a colon, you should always put at least one space afterwards.  (Some typists teach that you should even put two spaces after a colon, but I have never followed this.)  In any case, I would consider a colon without a space after it an error.  This solves this ambiguity issue imho.

--[[ChuckSmith]], 2007-Feb-27

Shall I search Wikipedia and show you how many people don't put a space after the colon? :)

-- [[RadomirDopieralski]], 2007-02-2007

Plain URLs without markup aren't supposed to be converted automatically to links, are they?

If they aren't, I suggest we stick with that. It's easy enough to add brackets, and there will always
be cases where the engine won't recognize a whole URL correctly. I've already seen such cases
on this site.

-- [[YvesPiguet]], 2007-02-27

They are. I remember arguing against it initially, but I changed my mind and actually would argue **for** it now. It's the sane thing to do if you can avoid false positives (and you can, by listing the protocolas accepted).

-- [[RadomirDopieralski]], 2007-02-27

Ok, thanks, I see it's in [[Creole 0.5]] but not in [[Links]].

I guess I must look unsane; I have
the same concerns as Jared wrt unrecognized protocols (do you support the whole list at
[[http://www.iana.org/assignments/uri-schemes.html]]? but even {{{afp:}}}
(Apple File Protocol) or {{{call:}}} aren't there.)

I guess I'm asking too much to Creole: not only a kind of average between existing syntaxes,
but something unambiguous, well defined, consistent, not outsmarting the user, and with
a good balance between simplicity and power.

-- [[YvesPiguet]], 2007-02-27