highlight & symbol as illegal where it generates "Misplaced alignment tab character &" error on compile

[tbates]

Hi given some text

 this & that.

The user will get a compile error — Misplaced alignment tab character &.

It would be great to have this flagged in the grammar if possible.

[ciandorr]

Seconded, that would be easy to add. Non-escaped & characters generate an error unless they are inside certain environments, including tabular, tabularx, eqnarray, align, and aligned, and I often forget to delete them when I am switching from align to equation.