<%$, <%@, <%=, <%# ... what's the deal

asp.netserver-tags

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?

Best Answer

<% %> - 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

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Asp.net-mvc – A potentially dangerous Request.Form value was detected from the client

I think you are attacking it from the wrong angle by trying to encode all posted data.

Note that a "<" could also come from other outside sources, like a database field, a configuration, a file, a feed and so on.

Furthermore, "<" is not inherently dangerous. It's only dangerous in a specific context: when writing strings that haven't been encoded to HTML output (because of XSS).

In other contexts different sub-strings are dangerous, for example, if you write an user-provided URL into a link, the sub-string "javascript:" may be dangerous. The single quote character on the other hand is dangerous when interpolating strings in SQL queries, but perfectly safe if it is a part of a name submitted from a form or read from a database field.

The bottom line is: you can't filter random input for dangerous characters, because any character may be dangerous under the right circumstances. You should encode at the point where some specific characters may become dangerous because they cross into a different sub-language where they have special meaning. When you write a string to HTML, you should encode characters that have special meaning in HTML, using Server.HtmlEncode. If you pass a string to a dynamic SQL statement, you should encode different characters (or better, let the framework do it for you by using prepared statements or the like)..

When you are sure you HTML-encode everywhere you pass strings to HTML, then set ValidateRequest="false" in the <%@ Page ... %> directive in your .aspx file(s).

In .NET 4 you may need to do a little more. Sometimes it's necessary to also add <httpRuntime requestValidationMode="2.0" /> to web.config (reference).

Javascript – Change the selected value of a drop-down list with jQuery

jQuery's documentation states:

[jQuery.val] checks, or selects, all the radio buttons, checkboxes, and select options that match the set of values.

This behavior is in jQuery versions 1.2 and above.

You most likely want this:

$("._statusDDL").val('2');

Best Answer

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Asp.net-mvc – A potentially dangerous Request.Form value was detected from the client

Javascript – Change the selected value of a drop-down list with jQuery

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