<%$, <%@, <%=, <%# … what's the deal?

Question

I've programmed in both classic ASP and ASP.NET, and I see different tags inside of the markup for server side code.

I've recently come across a good blog on MSDN that goes over the difference between:

• <%= (percentage together with equals sign) and
• <%# (percent sign and hash/pound/octothorpe)

(<%# is evaluated only at databind, and <%= is evaluated at render), but I also see:

• <%$ (percent and dollar sign) and
• <%@ (percent sign and at symbol).

I believe <%@ loads things like assemblies and perhaps <%$ loads things from config files? I'm not too sure.

I was just wondering if anyone could clarify all of this for me and possibly explain why it's important to create so many different tags that seemingly have a similar purpose?

Answer 1

• <% %> - is for inline code (especially logic flow)
• <%$ %> - is for evaluating expressions (like resource variables)
• <%@ %> - is for Page directives, registering assemblies, importing namespaces, etc.
• <%= %> - is short-hand for Response.Write (discussed here)
• <%# %> - is used for data binding expressions.
• <%: %> - is short-hand for Response.Write(Server.HTMLEncode()) ASP.net 4.0+
• <%#: %> - is used for data binding expressions and is automatically HTMLEncoded.
• <%-- --%> - is for server-side comments

Answer 2

You've covered 2 of them (<%# is evaluated only at databind, and <%= is evaluated at render), and the answer for "<%@" is that it's compiler directives (ie., stuff like what you'd put on a compiler's command line).

I don't know about "<%$".