This is perhaps not a very intelligent question, as I am not (of great intelligence nor) well versed in raw tex, even more so \catcode
but in the code given in a previous answer there is a use of \catcode
:
\newcommand*\pFqskip{8mu}
\catcode`,\active
\newcommand*\pFq{\begingroup
\catcode`\,\active
\def ,{\mskip\pFqskip\relax}%
\dopFq
}
\catcode`\,12
\def\dopFq#1#2#3#4#5{%
{}_{#1}F_{#2}\biggl[\genfrac..{0pt}{}{#3}{#4};#5\biggr]%
\endgroup
}
Is there a reason why the first
\catcode`,\active
has no backslash and the later ones do? This former answer explains that the backslash is for "special catcode" characters, whate'er that may be, but why is it omitted in the first instance and not the second?
Then of course, my real question is what is the \catcode
's purpose there? I roughly understand what an active character is, but not its role in the code. Would it perhaps explain why when I use the command as follows:
\pFq{3}{2}{a,b,c}{d,e}{z}
I get no commas between the a, b, and c, or the d and e, as I would prefer?
[update, I think I just figured it out that the first part redefines comma to be small skips, given by \pFqskip{8mu}
, but I am not sure why, but I can see why this would cause the commas to disappear.]
Again, probably elementary questions, but I am a bear of little TeX.