The luamathalign package for LuaLaTeX

With amsmath's align environment simple equations can be aligned easily, e.g.

2  &=1+1\\
2-1&=1

but even just adding an underline makes this much more complicated. E.g.

2  &=1+1\\
\underline{2-1&=1}

is not allowed. Similarly alignment points surrounded by \left and \right or points nested in other environments do not work.

For LuaLaTeX this can be solved with luamathalign. It adds a command \AlignHere which behaves mustly like & except that it's allowed almost anywhere. E.g.

                      2 &= 1+1\\
\underline{2-1 \AlignHere= 1}

Licensed under the LPPL v1.3c or later.