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Summary: Well, it //almost// works, but is not very elegant (and has a visible side effect). First of all, TeX discards trailing spaces, so "{{{\ }}}" at . . .
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> Well, it //almost// works, but is not very elegant (and has a visible side effect).
> First of all, TeX discards trailing spaces, so "{{{\ }}}" at the end of line becomes effectively a backslash-newline (which happens to //expand// to---but not //mean//---"{{{\ }}}"---see line b158 of the LaTeX2e source). (You may say "{{{\ %}}}" if you don't want TeX to discard that space.)
> Further, all whitespace is discarded in vertical mode (and after a {{{\\}}}, TeX is indeed in vmode), but "{{{\ }}}" is //not// considered to be "whitespace" here---instead, it's a //horizontal// command putting a space on a horizontal list. So we get a spurious space at the beginning of the next line. (Try {{{\tracingcommands=1\tracingmacros=1\tracingonline=1}}} if you want to see it for yourself!)
> I believe that {{{\relax}}} is the cleanest way to solve this problem. It's not very "LaTeX-ish", since {{{\relax}}} is rather a low-level TeX primitive, but I can't think of any "better" alternative.
> Notice also that a similar problem in {{{amsmath}}} displayed environments is solved by the {{{mathtools}}} package.
> -- Marcin Borkowski 2010-09-12 23:31 UTC
wouldn’t a “\ “(backslash-space) have worked also?
– tj 2010-09-12 12:43 UTC
Well, it almost works, but is not very elegant (and has a visible side effect).
First of all, TeX discards trailing spaces, so “\ ” at the end of line becomes effectively a backslash-newline (which happens to expand to—but not mean—”\ ”—see line b158 of the LaTeX2e source). (You may say “\ %” if you don’t want TeX to discard that space.)
Further, all whitespace is discarded in vertical mode (and after a \\, TeX is indeed in vmode), but “\ ” is not considered to be “whitespace” here—instead, it’s a horizontal command putting a space on a horizontal list. So we get a spurious space at the beginning of the next line. (Try \tracingcommands=1\tracingmacros=1\tracingonline=1 if you want to see it for yourself!)
I believe that \relax is the cleanest way to solve this problem. It’s not very “LaTeX-ish”, since \relax is rather a low-level TeX primitive, but I can’t think of any “better” alternative.
Notice also that a similar problem in amsmath displayed environments is solved by the mathtools package.
– Marcin Borkowski 2010-09-12 23:31 UTC