[texhax] 'continue to next line' control sequence?

[Eduardo M KALINOWSKI]

Oleg Katsitadze escreveu:
> Some nitpicking:
>
> On Mon, Jul 30, 2007 at 03:35:55PM -0300, Eduardo M KALINOWSKI wrote:
>   
>> Whitespace around the column separator & is irrelevant.
>>     
>              ^^^^^^
>              after
>
> This small plain TeX example shows this:
>
> ------------------------------>%------------------------------
> \halign{
> #&#\cr
> a&b\cr
> }
>
> \halign{
> #&#\cr
> a &b\cr
> }
>
> \halign{
> #&#\cr
> a& b\cr
> }
>
> \bye
> ------------------------------%<------------------------------
>   
You're right in that. However, Latex does ignore whitespace before the 
&, as this shows:

---8<---
\documentclass{article}
\begin{document}

\begin{tabular}{ll}
a&b
\end{tabular}

\begin{tabular}{ll}
a &b
\end{tabular}

\begin{tabular}{ll}
a& b
\end{tabular}

\end{document}
---8<---

The result is different because of the automatic column spacing, but all 
three tabular's are equal. And this makes me wonder how exactly can 
Latex achieve that effect?