isalnum, isalpha, isdigit, isxdigit, isspace
Synopsis:
$isalpha(
$isdigit(
$isxdigit(
$isalnum(
$isspace(
Technical:
These functions 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. 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