Returns the length of the initial segment of
str1 which consists entirely of characters
in str2.
The line of code:
will assign 2 to$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.
注意: 本函数可安全用于二进制对象。
See also strcspn().