type missing_feature =Features which are not available in all versions of the frontend
exception Migration_error of missing_feature * Location.tException thrown by migration functions when a feature is not supported.
val missing_feature_description : missing_feature -> stringmissing_feature_description xis a text describing the featurex.
val missing_feature_minimal_version : missing_feature -> stringmissing_feature_minimal_version xis the OCaml version where x was introduced.
val migration_error_message : missing_feature -> stringTurn a missing feature into a reasonable error message.