@cityjson/flatcitybuf
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    Variable OPEN_PREFETCH_SIZEConst

    OPEN_PREFETCH_SIZE: 12944

    2024 + (1 + 16 + 256) * 40 = 12944 bytes: an assumed 2 KB header plus the top three R-tree levels at the format's default branching factor of 16. Format Reference, "HTTP constants"; http_reader/mod.rs:80-98. One request at open() for this many bytes buys magic + header + those three levels without a second round trip, for files whose header and index top are that shallow.