ASP.NET configuration files are XML-based text files--each named web.config--that can appear in any directory on an ASP.NET Web application server. Each web.config file applies configuration settings to the directory it is located in and to all virtual child directories beneath it. Settings in child directories can optionally override or modify settings specified in parent directories. The root configuration file--WinNT\Microsoft.NET\Framework\
If a web.config file is present at the root directory for a site, for example "Inetpub\wwwroot", its configuration settings will apply to every application in that site. Note that the presence of a web.config file within a given directory or application root is completely optional. If a web.config file is not present, all configuration settings for the directory are automatically inherited from the parent directory.
Configuration Section Handlers and Sections
A web.config file is an XML-based text file that can contain standard XML document elements, including well-formed tags, comments, text, cdata, and so on. The file may be ANSI, UTF-8, or Unicode; the system automatically detects the encoding. The root element of a web.config file is always a
1) Configuration section handler declarations
2) Configuration section groups and
3) Configuration section settings