<% if (User.IsInRole("admin")) { %>
You can see this
<% } else { %>
You are no admin fool!
<%} %>
http://msdn2.microsoft.com/en-us/library/ms178135(vs.80).aspx
<%= ... %>
Used for small chunks of information, usually from objects and single pieces of information like a single string or int variable:
The Date is now <%= DateTime.Now.ToShortDateString() %>
The value of string1 is <%= string1 %>
http://msdn2.microsoft.com/en-us/library/6dwsdcf5(VS.71).aspx
*note: <%= is the equivalent of Response.Write()
<%# .. %> Used for Binding Expressions; such as Eval and Bind, most often found in data controls like GridView, Repeater, etc.:
http://msdn2.microsoft.com/en-us/library/ms178366.aspx
<%$ ... %>
Used for expressions, not code; often seen with DataSources:
http://msdn2.microsoft.com/en-us/library/d5bd1tad.aspx
<%@ ... %>
This is for directive syntax; basically the stuff you see at the top your your aspx pages like control registration and page declaration:
<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Title="Untitled Page" %>
<%@ Register TagPrefix="wp" Namespace="CustomWebParts" %>
http://msdn2.microsoft.com/en-us/library/xz702w3e(VS.80).aspx
<%-- ... --%>
This is a server side comment, stuff you don't want anyone without code access to see:
<%-- sometimes end users make me angry --%>
http://msdn2.microsoft.com/en-us/library/4acf8afk.aspx
