The | operator groups left-to-right.

The operands shall be of integral or unscoped enumeration type.

The usual arithmetic conversions ([expr.arith.conv]) are performed.

Given the coefficients and
of the base-2 representation ([basic.fundamental])
of the converted operands x and y,
the coefficient
of the base-2 representation of the result r
is 1 if at least one of and are 1, and 0 otherwise.