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The prefix IHO identifies it as an IHO document.
IHO
IHO B-4
Some IHO standards have multiple editions:
IHO S-100 1.0.0 IHO S-100 2.0.0
Some IHO standards have multiple volumes:
IHO P-1/21 IHO P-1/22
IHO S-65AnnexA 1.0.0
