This project is a proof-of-concept (POC) for a read-only app.config elements inheritance in a custom configuration section.
Inspired by MSBuild's properties and items placeholders (e.g., $(Platform) and @(Compile) placeholders).

The goal was to achieve reusing of existing configuration properties inside another configuration property; any configuration element should be able to define placeholders in its property's value that would reference its existing properties and/or properties that any of its parent configuration elements have.

For example, consider the following custom configuration section:

<UserSettings Application="MY APP"
              Version="1.0">
  <User FullName="$(FirstName) $(LastName)"
        FirstName="John"
        LastName="Doe"
        WelcomeMessage="Hello $(FullName), welcome to $(Application) v$(Version)!" />
</UserSettings>

The result of WelcomeMessage property is:

Hello John Doe, welcome to MY APP v1.0!

Notes:

• ☑︎ Added support for inherited values from ConfigurationElement.
• ☑︎ Added support for inherited values from ConfigurationElementCollection.
• ☑︎ Added support for inherited values from ConfigurationSection.
• ☑︎ Added support for global values from appSettings.
• ☑︎ Added support for Standard and Custom Numeric Format, e.g. $(placeholderName \# #,##0.00).
• ☑︎ Added support for Standard and Custom Date and Time Format, e.g. $(placeholderName \@ MMMM dd, yyyy).