Returns the length of the initial segment of
str1 which consists entirely of characters
The line of code:
$var, because the string "42" will be the longest segment containing characters from "1234567890".
As of PHP 4.3.0, strspn() accepts two optional
integer parameters that can be used to define the
start position and the
length of the string to examine.
Note: This function is binary-safe.
See also strcspn().