Andrew Sarangan writes:

An obvious example of this is restricted airspaces. The majority of
R-airspaces overlap with G or E airspaces, but in those instances we
don't question which rules apply.

They aren't airspace classes though. Class B and Class C are both
airspace classes; logically they cannot occupy the same space at the
same time.

Restricted and other special airspace is an additional qualifier that
supplements the existing airspace class, so they can coexist.

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