Minimum 6 characters regex expression

If I understand correctly, you need a regex statement that checks for at least 6 characters (letters & numbers)?

/[0-9a-zA-Z]{6,}/

This match 6 or more any chars but newline:

/^.{6,}$/

Something along the lines of this?

<asp:TextBox id="txtUsername" runat="server" />

<asp:RegularExpressionValidator
    id="RegularExpressionValidator1"
    runat="server"
    ErrorMessage="Field not valid!"
    ControlToValidate="txtUsername"
    ValidationExpression="[0-9a-zA-Z]{6,}" />