Streams with a minimum coded frame width or height below 16 should have a maximum parameters level

[rzumer]

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When the mapped level is contained in the tables above, it is a requirement of bitstream conformance that the following constraints hold:
(...)
FrameWidth is greater than or equal to 16
FrameHeight is greater than or equal to 16

While ambiguous, it is likely "the tables above" refers to the second and third tables in this section, which exclude undefined levels, reserved levels, and maximum parameters.