ASP.Net Regular Expression Validator to validate Minimum and Maximum Text Length

Minimum length 7 and Maximum length 10. Characters allowed – a - z A - Z 0-9 ’@ & # .

<asp:RegularExpressionValidator ID="RegExp1" runat="server"    

ErrorMessage="Password length must be between 7 to 10 characters"

ControlToValidate=" txtPassword "    

ValidationExpression="^[a-zA-Z0-9'@&#.\s]{7,10}$" />