How is
<None Include="C:\foo.bar" />
different from
<Content Include="C:\foo.bar" />
?
The MSDN article on the build action property explains the differences.
None - The file is not included in the project output group and is not compiled in the build process. An example is a text file that contains documentation, such as a Readme file.
Content - The file is not compiled, but is included in the Content output group. For example, this setting is the default value for an .htm or other kind of Web file.