Meshing

I have built up a composite layer set (real constant 1) it is called, it consists of 4 materials. I am attempting to apply it with a mesh using the shell 99 linear element type.

When I attempt to mesh an area using the "mesh tool" I have an option "area attributes" where i can choose the material number, the element number and the real constant set number.

This is where i am confused, Why do i have to choose a material number and also a real constant set number. All i want to choose is a real constant set number as this will contain 4 materials (the composite), and I should not have to also specify one material number as i have already specified my materials in the real constant set?? this is a contradiction!