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

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.

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

