Groups related definitions for use in expr. Each definition is evaluated in order, and finally the body expr is evaluated. Only the expressions within the local form (including the right-hand-sides of the definitions and the expr) may refer to the names defined by the definitions. If a name defined in the local form is the same as a top-level binding, the inner one “shadows” the outer one. That is, inside the local form, any references to that name refer to the inner one.