Numeric Date Validation

It has appeared that ancient sources give a method for Numeric Date
Validation that involves numerous tests to determine month length;
versions are often posted by incomers here. That sort of code seems
unnecessarily long.

For some while, the following approach has been given here :-

function ValidDate(y, m, d) { // m = 0..11 ; y m d integers, y!=0
with (new Date(y, m, d))
return (getMonth()==m && getDate()==d) }

and it may remain the shortest code. But it does require, in every
case, the creation and disposal of a Date Object.

The following is about 50% longer in code, but about four times faster
in my system - and it seems to be right, too.

function DateOK(Y, M, D) {
return D>0 && (D<=[,31,28,31,30,31,30,31,31,30,31,30,31][M] ||
D==29 && M==2 && Y%4==0 && (Y%100>0 || Y%400==0) ) }

Note that checking for 1 <= M <= 12 is inherent, and that the Leapness
of the year is only determined if the date given is February 29th.

Also, it is easy to use only the quadrennial rule if it is certain that
dates are in 1901-2099, or only two rules for 2001-2399.