Anything can clank with anything with the right timing aside from aerials.
that isn't true at all. try beating pound or bowser's fsmash a falcon punch. there are a punch of moves that can't be out prioritized really.
Okay, just to clarify.
There are two major kinds of hitboxes:
the ones that CAN clash (most attacks)
and the ones that CAN'T (e.g. Meta Knight's aerial normals, Sheik's needles)
regardless of what kind of an attack it is, the hitboxes that CAN'T clash will not clash even if the following rules state that it should.
Ground normals can clash with other ground normals and specials.
Aerial normals can clash with specials.
Specials can clash with ground normal, aerial normals, and specials.
Glide attacks are classified as specials.
With the exception of clashing with specials, which can clash regardless of damage difference, attacks will only clash if they are within 10% damage of each other.
If a ground normal clashes, its animation is immediately canceled. The exception to this is clashing with a special, in which case the animation will continue, and the attack's hitbox is "nullified" unless the difference between the attack and the special it clashed with is greater than 10%.
If an aerial normal clashes, its animation continues but the attack's hitbox is "nullified."
If a ground special clashes, its animation is immediately canceled. If an aerial special clashes, the animation continues but that hitbox is "nullified."