MivaScript Builtin Function, Miva Merchant 9+
len_var( string var ) <mvt:assign name="g.return_value" value="len_var( string var )" />
Returns the number of characters in string. This function is identical to len() but its parameter is passed by reference, improving performance when dealing with large strings.
a literal string value embedded in single quotes or an expression that evaluates as a string.