Btukfyl

This question includes a solution but I really want to know why it works and why what "should" work doesn't I think my MWE says is all:

documentclass[12pt]{article}

usepackage{siunitx}

% TeX Live 2015 (Ubuntu 18.04)

% siunitx Ver 2.6m

sisetup{

group-digits=integer,

group-minimum-digits={3},

group-separator={,} % NOT ","

}



begin{document}



After  looking at a number of examples (and the

documentation) I could not got what I wanted

(3,000). If group-separator is set to verb:{,}: 

the thousands separator is a space. But if set to

"," it works.



begin{tabular}{ccc}

Code in document    &              & Typeset as\

hline

verb:num{3000}:    &  num{3000}  & 3,000\

verb:$num{3000}$:  & $num{3000}$ & 3,000\

verb:num{$3000$}:  & does not work\

end{tabular}

end{document}

The token , is not an “escaped comma”, but a command on its own, which means “insert a thin space (one sixth of an em). With

group-separator={whatever}

the separation between groups is set to whatever. Thus with

group-separator={,}

you'll get a comma, but with

group-separator={,}

you'll get a thin space.

The braces are only mandatory with the comma, otherwise the option parser would get confused.