checkPropertyOverride() compared type, visibility, set-visibility,
readonly and final between a child property and the parent's, but never
Modifiers::STATIC. Redeclaring `public static int $x` as
`public int $x` (or the reverse) was accepted, while Zend fatals with
"Cannot redeclare static A::$x as non static B::$x" (and "Cannot
redeclare non static ... as static ..." in the other direction):
static and instance properties are different kinds of storage and can
never override one another.
Alessio Giacobbe