val default : (Ppx_core.label_declaration, Ppx_core.expression) Ppx_core.Attribute.t
val drop_default : (Ppx_core.label_declaration, Ppx_core.unit) Ppx_core.Attribute.t
val drop_if : (Ppx_core.label_declaration, Ppx_core.expression) Ppx_core.Attribute.t