multiline text box exceed the max lenght property. max length not working in multiline text box

using javascript 
make a function 
  <script language="javascript" type="text/javascript">
        function textboxMultilineMaxNumber(txt,maxLen){
    try{
    if(txt.value.length > (maxLen-1))return false;
    }catch(e){
    }
    }
    </script>
In control 

<asp:textbox id="txtMl" runat="server"  TextMode="MultiLine"
onkeypress="return textboxMultilineMaxNumber(this,10)"></asp:textbox>  comment// 10 is max lenght.

on server side validation 

  <asp:textbox id="txtMl" runat="server"  TextMode="MultiLine"></asp:textbox> 

 <asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" ControlToValidate="txtMl"
                    Display="Dynamic" ErrorMessage="Please limit to 10 characters or less."
                    ValidationExpression="[\s\S]{1,10}"></asp:RegularExpressionValidator>
                    <asp:Button ID="btnrun" Text="Test" runat="server" />