'ConfigurationManager.GetSection' is not backwards compatible for nested sections

[julealgon]

After migrating from System.Configuration's ConfigurationManager into AnyConfig's, I started to get errors related to nested XML sections that were previously working with the legacy class.

Here is an example:

var customErrors = (CustomErrorsSection)ConfigurationManager.GetSection("system.web/customErrors")

  <system.web>
    <compilation debug="true" targetFramework="4.8" />
    <httpRuntime targetFramework="4.8" maxQueryStringLength="32768" maxUrlLength="65536" maxRequestLength="524288000" enableVersionHeader="false" />
    <customErrors mode="Off" />
    <globalization culture="auto:en-US" uiCulture="en" />
  </system.web>

Notice how we are fetching the customErrors section inside system.web. The call works as expected when using the legacy class, but returns null using AnyConfig's implementation.

If I change the code to read only the "system.web" section, it fetches the main section correctly.

I believe this is a gap in the backwards compatibility of the ConfigurationManager class.