Operator priority

According to the (non-normative) information at
https://www.w3.org/TR/MathML3/appendixc.html, the expression:

    *a* = *b* ⇒ *b* = *c*

should be parsed as

    *a* = (*b* ⇒ *b* = *c*)

since = has a priority of 260 and ⇒ a priority of 270.

Similarly, all the arrows have the same priority, so that

    P → Q ⇎ Q → P

would not parse as

    (P → Q) ⇎ (Q → P)

as one might expect.

What was the rationale behind these priority values?

Best,
Arno.