<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- объявление секций -->
  </configSections>

  <!-- системные секции -->
  <startup>...</startup>
  <runtime>...</runtime>
  <System.web>...</System.web>
  <System.serviceModel>...</System.serviceModel>
  <System.Data>...</System.Data>

  <!-- пользовательские секции -->
  <appSettings>...</appSettings>
  <userSettings>...</userSettings>
  <connectionStrings>...</connectionStrings>

  <!-- кастомные секции -->
  <mySection type="MyNamespace.MySectionHandler, MyAssembly">...</mySection>
</configuration>