uncomplete Eiffel-code?

[system]

Hi,

While reading the eiifel code I find in
ref_impl_eiffel/libraries/openehr/src/am/archetypes/assertion/expr_constraint.e
that in this class is a property "expression" of type ADL_EXPR_ITEM

I cannot find the implementation of this class ADL_EXPR_ITEM, maybe missing?

thanks
Bert