Hidden Project Files in Solution Explorer
There are several Visual Studio Tools for Office project files that are hidden in Solution Explorer by default. These files appear when you click Show All Files. For more information, see Solution Explorer. The extensions for the files are .designer.xml, and .designer.vb or .designer.cs. These files are generated by Visual Studio Tools for Office, based on the document structure.
Do not modify these files. Modifications to hidden files are not supported.
File Generation
The generated files are completely regenerated whenever certain changes occur in the document. If you make any changes to these files manually, those changes will be lost the next time the file is regenerated. For that reason, they are included mainly for reference purposes.
See Also
Concepts
Office Documents in the Visual Studio Environment Overview
Office Menus in the Visual Studio Environment