A single, version-stamped migration. version is the system version at which
the migration is introduced; the runner applies every step whose version is
newer than the world's stored migration version and no newer than the running
system version. migrators holds one function per in-scope document kind the
step needs to touch — omit a kind the step does not change.
A single, version-stamped migration.
versionis the system version at which the migration is introduced; the runner applies every step whose version is newer than the world's stored migration version and no newer than the running system version.migratorsholds one function per in-scope document kind the step needs to touch — omit a kind the step does not change.