PHP: Validating Numeric Values and Digits

I've inherited a lot of code where the previous developer used PHP's is_numeric() and it's gotten them into trouble. There's a big difference between validating that a value is numeric and validating that a value is all digits. Here's how to validate the two:

/* numeric, decimal passes */
function validate_numeric($variable) {
 return is_numeric($variable);
}

/* digits only, no dots */
function is_digits($element) {
 return !preg_match ("/[^0-9]/", $element);
}

A customer number, for example, should not have any decimal points but using is_numeric() would let a decimal value pass the test. Don't be this guy!