About $ character in asp.net

I have a code section below :

    <asp:SqlDataSource ID="SqlDataSource1" runat="server"
  ConnectionString="<开发者_JAVA技巧%$ ConnectionStrings:MainConnStr %>"
  SelectCommand="SELECT [au_id], [au_lname], [au_fname], [state] FROM [authors]" />

What is meaning of The $ character in value of ConnectionString attribute?

It's referred to as an ASP.NET Expression. You can pull config information such as ConnectionStrings or AppSettings as well as Resources.

ASP.NET Expressions Overview

They're expressions, read about them here

Read about all inline tags here