Controlling tag placement in arrays

From https://groups.google.com/d/msg/mathjax-users/bSDEfRKEfAo/3qAcaXgnXI8J

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Q2 : Source (after Davide Cervone ) :

$$ (Z) ~~~~~~~~~~~~
  \left\{ \begin{array}{l}
    Row 1 , \\\\
    Row 2 , \\\\
    Row 3 ;
  \end{array} \right.
$$

Is it possible, without HTML, to get the "(Z)" placed at the left margin (still aligned with Row 2), with the brace and the array centred, as may be seen in http://www.ltas-vis.ulg.ac.be/cmsms/uploads/File/Lagrange_essai_3corps.pdf page 231 (the third page; PDF ~ 5MB) ?

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For Q2, the best solution is to use

$$
 \left\{ \begin{array}{l}
   Row 1 , \\\\
   Row 2 , \tag{Z} \\\\
   Row 3 ;
\end{array} \right.
$$

which will label the second row with "(Z)" (the parentheses are added automatically by \tag). Then change the TagSide parameter in the TeX section of your configuration to "left" (it is "right" by default). E.g.,

<script type="text/x-mathjax-config">
MathJax.Hub.Config({
 TeX: {TagSide: "left"}
});
</script>

Of course, you can combine the two configuration changes into one MathJax.Hub.Config() call (but be careful to have the commas separating this correct, with no extra one at following the last item or it won't work in some versions of IE).

Hope that takes care of things for you.

Davide