IT:AD:Elmah:HowTo:Install and Configure (original)

It will modify the config file to define a section:

  <configSections>
    <sectionGroup name="gotdotnet.elmah">
      <section name="errorLog" 
        type="System.Configuration.SingleTagSectionHandler, System, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
    </sectionGroup>
  </configSections>

Elmah is a HttpModule, so it's basically doing the following:

<httpModules>
  <add name="ErrorLog" type="GotDotNet.Elmah.ErrorLogModule, 
    GotDotNet.Elmah, Version=1.0.5527.0, Culture=neutral, 
    PublicKeyToken=978d5e1bd64b33e5" />
</httpModules>

It's also installing a handler

  <system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <handlers>
      <remove name="ELMAH" />
      <add name="ELMAH" verb="POST,GET,HEAD" path="elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah" />
      ...
      

Which IT:AD:ASP.NET:MVC ignores by default in the App_Start/RouteConfig.cs:

routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

• https://msdn.microsoft.com/en-us/library/aa479332.aspx