In PHP documentation rand() and mt_rand() parameters are 
specified as "([int min [, int max]])" which implies max is 
optional when min is specified, so that rand(256) would 
return a number ranging from 256 to getrandmax().

This is not supported however. Looking at rand.c, it looks 
like the author partially implemented this and forgot to 
add the relevant code to the portion that parses the 
parameters on both functions.