The <appSettings> section is one of many predefined configuration sections provided by the .NET Framework. Programmers can also create their own sections. To create a new section, you need to accomplish two basic tasks: declare the section in the <configSections> block, and fill the section with custom data.
One of the key bits of information you need to specify while declaring a new section is the name of the section handler class. The section handler class can be one of the predefined classes provided by the .NET Framework or a class that you write from scratch or inherit from an existing class. The section handler object is responsible for reading and parsing the actual contents of the setting.