Do you know what "sour grapes" means figuratively?
In very tall buildings they usually have "express" elevators that only stop at certain floors. Or elevators that serve between the main (ground) floor and a range of floors above.
Much like taking trains. A "local" stops at every stop on the line. An "express" only stops at larger, strategic stations.
With the elevators, a "semi-local" would be "local" service, but only for a range of floors. It is not "local" service for the entire building.
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