谁能解释下啊？<%$ %> 这是什么意思啊？送分10分，谢谢！！！！！！！！
aspx里：

    <form   id= "form1 "   runat= "server ">
        <asp:GridView   ID= "GridView1 "   DataSourceID= "SqlDataSource1 "   runat= "server "   />
        <asp:SqlDataSource   ID= "SqlDataSource1 "   runat= "server "  
            SelectCommand= "SELECT   [au_id],   [au_lname],   [au_fname],   [phone],   [address],   [city],   [state],   [zip],   [contract]   FROM   [authors] "
            ConnectionString= " <%$   ConnectionStrings:Pubs   %> "   />
    </form>


webconfig里：

<connectionStrings>
        <!--
        This   connection   is   inherited   from   the   ASP.NET   Quickstart   Web.config   file
        Uncomment   this   section   to   edit   the   sample   locally

        <add   name= "Pubs "   connectionString= "Server=(local)\SQLExpress;Integrated   Security=True;Database=pubs;Persist   Security   Info=True "
            providerName= "System.Data.SqlClient "   />
        <add   name= "Northwind "   connectionString= "Server=(local)\SQLExpress;Integrated   Security=True;Database=Northwind;Persist   Security   Info=True "
            providerName= "System.Data.SqlClient "   />
        <add   name= "Contacts "   connectionString= "Server=(local)\SQLExpress;Integrated   Security=True;Database=Contacts;Persist   Security   Info=True "
          providerName= "System.Data.SqlClient "   />
        -->
        <add   name= "NorthwindOLEDB "   connectionString= "Provider=Microsoft.Jet.OLEDB.4.0;Data   Source=|DataDirectory|Northwind.mdb; "
          providerName= "System.Data.OleDb "   />
        <add   name= "ContactsDatabase "   connectionString= "Data   Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|Database.mdf;Integrated   Security=True;User   Instance=true; "
          providerName= "System.Data.SqlClient "   />
  </connectionStrings>
        <system.web>
                <pages   styleSheetTheme= "Default "/>
                <caching>
                        <sqlCacheDependency   enabled= "true "   pollTime= "1000 ">
                                <databases>