dotnet/aspnetcore#7555
The file format is very similar to the item.
Before: build\netcoreapp3.0\Microsoft.AspNetCore.App.props:
<ItemGroup>
<PackageConflictOverrides Include="Microsoft.AspNetCore.App">
<OverriddenPackages>
Microsoft.AspNetCore.Antiforgery|3.0.0-preview3-19111-04;
Microsoft.AspNetCore.Authentication.Abstractions|3.0.0-preview3-19111-04;
Microsoft.AspNetCore.Authentication.Cookies|3.0.0-preview3-19111-04;
// ...
After: build\netcoreapp3.0\Microsoft.AspNetCore.App.PackageOverrides.txt:
Microsoft.AspNetCore.Antiforgery|3.0.0-preview3-19111-04
Microsoft.AspNetCore.Authentication.Abstractions|3.0.0-preview3-19111-04
Microsoft.AspNetCore.Authentication.Cookies|3.0.0-preview3-19111-04
// ...
The identity of the item follows from the package/file name, the metadata is the body of the txt file, where newlines delimit instead of ; with whitespace ignored.