[magick-users] composite syntax

[Dado Feigenblatt]

I can't figure out the command line syntax to combine a series of tiles.
The tiles are all the same size of the resulting image,
i.e. they are mostly black with a small colored rectangle, so I can't 
'assemble'.
They also have alpha.
I think a simple 'over', 'add', or 'max' operation should do, but I 
can't get that to work in the command line.
I think I'm looking for something like
composite -compose 'add' (tiles*) out.png
Am I any close?

Thanks.
Dado