Rules for array keys

The whim wants to change the naming rules for the keys of the array to see if the computer will explode and produce the following results:

Increment starting from 3 if the first array key is not defined after 3=>a,b,c

If the key repeats the declaration then the latter content overrides the signature

If the key is not declared from 0123: Start incrementing

Keys can be integers and strings are invalidated if it is a floating-point type then an integer if the string happens to be an integer

But I know what the eggs are for.

Rules for array keys