visualstudio如何知道当前项目的类型？

In Visual Studio, the context menu command for adding an element in a WinForms project is different by the one showed for a WPF project. In fact, I can see "Add->Windows Form" in the first and "Add->Window" in the second. By which parameter/configuration VisualStudio can differentiate which kind of project is currently opened? My first bet was the .csproj file but I can see nothing distinctive about the project type.In Visual Studio, the context menu command for