An external identity (that you may get from OCLOperators_externalId) will be resolved to the object.

This will also be kind enough to try a few different alternatives to the externalid:

1. If we have a Guid called Guid (typed as Guid or string) property and it matches the sent-in value, we resolve.
2. If we sent in TheClassName;number, we will take the internal class id from the name and then try to resolve the result as externalid

See also: The_ExternalId_explained