Volume 1, page 58 in Chapter 2, Tools of Your Trade:
String Functions: The VAL Function
The ?TYPE MISMATCH ERROR listed for the VAL function does not occur; instead:
1. If the string begins with a non-numeric (except leading spaces) the value
returned is 0.
2. If the string begins with a number but contains non-numeric characters then
the value returned is the value of the beginning number.
The VAL of a null string is UNDEFINED! Because of the hard coding, Applesoft
returns 0. But the RAM-based Business Basic returns whatever value happens to
be in RAM memory at the time.