Returns the portion of a string specified by the $start and $length parameters.
If $start is negative, the returned string will begin at $start characters from the end of $val.
If $val is less than or equal to $start characters in length, FALSE will be returned.

<!--parser:xtscript-->
var $string = abcdefghijklm
var $portion = call substr $val=$string; $start=4 ; $length=6
print string = $string<br />
print portion = $portion 
<!--/parser:xtscript-->