In STM32L4 for CRC, what does it mean "Even polynomials are not supported"

[ABier.1]

In the Reference Manual for the STM32L41xxx/42xxx/43xxx/44xxx/45xxx/46xxx MCUs for the CRC Unit, it casually mentions "Even polynomials are not supported." But what does this exactly mean? Does it mean polynomials which have even parity are not supported (see https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Polynomial_representations_of_cyclic_redundancy_checks)? Or does it mean just polynomials with only even terms are not supported (e.g. x^4 + x^2 + 1) ?

[Tesla DeLorean]

No, most likely that both the high and low bit in the polynomial are 1

ie x^4 + x^2 + 1 -> 10101

That way the feedback term, for either direction goes into the end of the register as it shifts.