Page Directives:

A Page directive is a set of instructions given to ASP.NET compiler/parser. It is used to define the behavior of Web Forms. The page directive is always specified at the top of the page.

@Page Directive

The @Page directive is used to declare attributes that are specific to a .aspx page. It is used by the ASP.NET page compiler.

The General Syntax of a page directive is:
<%@ Page attribute=”value” [attribute="value"...] %>

Attributes of @Page Directive:

Specified below are some of the commonly-used attributes of an @Page Directive:

Language:
Example: <%@ Page Language=”C#” %>
The language (C# or VB) used to complie the code-behind file or current page is specified here. This is the language in which the code in the page or the code-behind file is written (inline and block).
Value can be “Visual Basic”, “C#”, or any other .NET supported language. A page can be written only in one language.

CodeFile:
Example: <%@ Page CodeFile=”Default.aspx.cs” %>
The name of the code-behind file, with which the current file is associated, is specified here.

CompilationMode:
Example: <%@ Page CompilationMode=”Auto” %>
CompilationMode property is set to specify whether an ASP.NET page is compiled or not. The possible values are “Always”, “Auto” and “Never”. The default value is “Always”.
The value “Auto” is used to improve performance. This will prevent ASP.NET from compiling the page dynamically, if possible. The disadvantage of Auto property is that if the page that is excluded from compilation contains that code that must be compiled, an error results when the page is visited.

Title:
Example: <%@ Page Title=”My First ASP.NET Page” %>
This attribute sets the <title> of the page. The rendered page’s <title> tag will contain the value given here.
The above example results in ==> <title>My First ASP.NET Page</title>

Debug:
Example: <%@ Page Debug=”True” %>
Indicates whether the compiler should use debug symbols on page or not. Default mode is “False”. It has to be set to “True” for development purposes.
This setting has adverse effect on site performance, so once the development is over it is set to “False”.

EnableViewState:
Example: <%@ Page EnableViewState=”True” %>
A boolean value which specifies if view state is maintained across page requests. The default value is true.
It is set to “True” for the view state to be maintained.

There are several more @Page directive attributes. For more, the reader is recommended to visit the MSDN web site.