I have two lists: list A and list B. List A should have a new multiple choice lookup column that allows the user to choose items from both list A and list B. Is this even possible? I have a kind of idea how to make a custom ASPX form in which the user would be able to choose from both list A and list B items, but I am completely clueless on how to make that multiple choice lookup column save a link to the list item located in the list B.
Edit: There is one restriction; this multiple choice lookup column needs to be filterable in the list A view.