MivaScript Builtin Function, Miva Merchant 9+
substring_var( string var, position, length )
<mvt:assign name="g.return_value" value="substring_var( string var, position, length )" />
Returns the substring of string, beginning at position start, length characters long. This function is identical to substring() but its first parameter is passed by reference, improving performance when dealing with large strings.
string var
position
length