This document can be viewed properly only in modern browsers with good support for CSS2 and the full HTML character set.
The LaTeX array column delimiter '&' used unadorned in
an embedded formula would be confused with the HTML use of the same character.
One solution is to type out the HTML character entity
'&' for the character:
| a11 | a12 | a13 |
| a21 | a22 | a23 |
| a31 | a32 | a33 |
The '&' can be used directly by wrapping the whole
LaTeX formula in a CDATA section:
| a11 | a12 | a13 |
| a21 | a22 | a23 |
| a31 | a32 | a33 |