Create structure and items, then refer them

I want to create a language where I can define some structure-like containers. In this example, I want MyOperation to refer a previously defined container, and Uses to be a list of Element from it (in this case, MyContainer A). I'm trying to help domain experts to be able to define these containers by helping them with autocomplete, etc.

MyContainer A {
 Element a
 Element b
}
MyContainer B {
 Element c
 Element d
}
MyOperation op {
 Refers :  A
 Uses {
 a, b
 }
}

How can this be accomplished?