Synopsis:
   $isalpha(<text>)
   $isdigit(<text>)
   $isnumber(<text> <base>>)

Technical:
   These function test whether the first character in the given string is
   an alphabetical character or a digit.  Only the first character is
   tested.
   
   The function $isnumber() is very similar to $isdigit(), except that
   it takes two arguments, the second specifying the numeric base of <text>.
   The second argument must be prefixed with a 'b'; eg. "b8" for base 8, "b16"
   for base 16. And as always, numbers in base 16 may be prefixed with "0x".

Practical:
   These functions are useful for testing an input string to see whether it
   is a number or a text string.  One use for this might be to check if it
   would be suitable input for $iptoname() or $nametoip().  Keep in mind
   that only the first character is tested, so this isn't a reliable way
   to see if the entire string is a number.

Returns:
   "true" or "false" value if first character is a letter or a digit

Examples:
   $isalpha(hello)         returns true
   $isalpha(2hello)        returns false
   $isdigit(123)           returns true
   $isdigit(2abc)          returns true
   $isdigit(a123)          returns false
   $isnumber(0x9FF b16)    returns true