tbook treats a `<math>`

element as an equation array, if it
consists of only *one* `<mtable>`

, with a `groupalign`
attribute *or* one or more `<mlabeledtr>`

rows. If you set
`groupalign="right center left"`

, this leads to an
`eqnarray` in LaTeX, and where ``&`' are in LaTeX,
you have to use `<maligngroup/>`

in MathML. Else the equations
are just stacked and not aligned.

But as already mentioned, you can also use `<m>`

inside
`<math>`

, which is very helpful for equation
arrays.

If you use these elements within a MathML equation array, you can
generate alignment markers (in LaTeX known as ``&`' signs)
with ``#`' signs^{1}. Put them where they would be in LaTeX. Although
MathML requires such a marker at the very beginning of an equation row,
this is not true for LaTeX, and not true for tbook.

Here is an example:^{2}

<math> <mtable groupalign="right center left"> <mtr> <mtd id="test"> <m> 1+1 #=# 2 </m> </mtd> <mtd> <m> 4 #=# 2 · 2 </m> </mtd> </mtr> </mtable> </math>

which is the same as LaTeX's

\begin{eqnarray} 1+1 &=& 2 \label{Test} \\ 4 &=& 2 \cdot 2 \nonumber \\ \end{eqnarray}

and you don't want to see the HTML/MathML output tbook must create for that.

(By the way, being the only child element of an `<mtd>`

,
`<m>`

is implicitly surrounded by an `<mrow>`

which is
necessary in this context.)

[1] because this is shorter than
`&`

[2] Actually both `<mtd>`

s should be in
*different* `<mtr>`

s according to the MathML specification.
You may do this, but it is just additional typing, since it doesn't
matter for tbook. However the MathML that tbook *produces*
is absolutely free of such sloppyness.