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Re: xparse and space skipping

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Wed, 11 May 2011 20:20:41 +0100

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 On 11/05/2011 20:01, Bruno Le Floch wrote: > Not quite true. For instance, amsmath redefined \\ not to skip spaces > when looking for an optional argument, I believe. And that works > because \\ is a control symbol, not a control word. I think this > choice of behaviour really needs to be supported, since it leads to > surprises for the end-user otherwise. > >> really correct! (At the same time, the implementation would be slightly >> easier to follow if this change was made.) > > On the other hand, emulating LaTeX2e arguments with space skipping > seems needed as well. Is it possible to get the best of the two worlds > with a "o_no_skip" argument specifier? Or more generally a modifier, > say K, which makes the next argument keep spaces (except perhaps for m > arguments where it should produce an error)? > > \DeclareDocumentCommand {\\} { Ks Ko } {...} We did do that at one point, but the problem then became that there is not a hard-and-fast rule. (While the AMS might be very clever in their redefinition, I'd prefer to be consistent with things like the classic "\item [" case even if it means rembering to do "\item{} [" and "\\{} [".) (As a user, I'd like to see one reliable syntax, and not have to read package documentation to explain why in one case "\foo{...} [...]" works but in another case "\baz{...} [...]" fails.) -- Joseph Wright