// a version on the left side is dropped.
//
// The -retract=version and -dropretract=version flags add and drop a
// retraction on the given version. The version may be a single version
// like "v1.2.3" or a closed interval like "[v1.1.0,v1.1.9]". Note that
// -retract=version is a no-op if that retraction already exists.
//
// The -godebug, -dropgodebug, -require, -droprequire, -exclude, -dropexclude,