Error with TikZ's Fitting Library when using coordinates

Question

I try to use the TikZ's Fitting Library with coordinates but it didn't compile.

In the manual of TikZ we got

This option must be given to a node path command. The coordinates or nodes should be a sequence of Tik Z coordinates or node names, one directly after the other without commas (like with the plot coordinates path operation). Examples as (1,0) (2,2) or (a) (1,0) (b), where a and b are nodes.

So I try

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}
\begin{tikzpicture}
    \node (foo) at (0,0) {foo};
    \node (bar) at (2,0) {bar};
    \node[draw, fit=(0,0) (2,0)] {};
\end{tikzpicture}
\end{document}

and got the following error:

! Undefined control sequence.
\pgfmathsetlength ...\pgfmath@onquick #2\pgfmath@ 
                                              {\begingroup \pgfmath@sele...
l.9         \node[draw, fit=(0,0) (2,0)]
                                     {};

If I use node labels instead of coordinates, as below, I got no error.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}
\begin{tikzpicture}
    \node (foo) at (0,0) {foo};
    \node (bar) at (2,0) {bar};
    \node[draw, fit=(foo) (bar)] {};
\end{tikzpicture}
\end{document}

I'm using

$ pdflatex --version
pdfTeX 3.1415926-2.4-1.40.13 (TeX Live 2012)
kpathsea version 6.1.0
...

with

$ tlmgr info pgf 
package:     pgf
...
installed:   Yes
revision:    22614
cat-version: 2.10
cat-date:    2010-10-27 12:56:09 +0200
cat-license: lppl1.3
collection:  collection-pictures
...

Answer 1

Use braces around co-ordinates - fit={(0,0) (2,0)}:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}
\begin{tikzpicture}
    \node  (foo) at (0,0) {foo};
    \node (bar) at (2,0) {bar};
    \node[draw, fit={(0,0) (2,0)}] {};
\end{tikzpicture}
\end{document}

The picture is ugly as the nodes will stretch beyond the co-ordinates to accommodate text.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}
\begin{tikzpicture}
    \node [draw=red,inner sep=0pt] (foo) at (0,0) {foo};
    \node [draw=red,inner sep=0pt] (bar) at (2,0) {bar};
    \node[draw=blue, fit={(0,0) (2,0)}] {};
\end{tikzpicture}
\end{document}

The better way is to use labels:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}
\begin{tikzpicture}
    \node [draw=red] (foo) at (0,0) {foo};
    \node [draw=red] (bar) at (2,0) {bar};
    \node[draw=blue, fit=(foo) (bar)] {};
\end{tikzpicture}
\end{document}

Here, the entire nodes are enclosed unlike the co-ordinates.