The idea is that the bits are to be tested to be determine if some error should be reported. So, the binary representation of E_ALL should be one in which various bits are set. However, for 32768, unlike 32767, only one bit is set
Note that you should not rely on these "magic numbers". Rather, use bitwise operators to "turn off" the errors reported, e.g., use E_ALL & ~E_NOTICE rather than the resulting value as a numeric constant.
