Are the four messages about the vsixmanifest when building a VS 2015 package normal?

I have noticed that the generated vsixmanifest file gets four build messages (in the error list window) when building the VSIX project, and wanted to know if these are 'normal' and can be ignored, or if there is something that can be done to avoid them.  The messages refer to 3 lines of the vsixmanifest file, as follows:

<Dependency Id="Microsoft.Framework.NDP" DisplayName="Microsoft .NET Framework" d:Source="Manual" Version="[4.5,)" />

gets the build message:

• Could not find schema information for the attribute 'http://schemas.microsoft.com/developer/vsx-schema-design/2011:Source'.

<Dependency Id="Microsoft.VisualStudio.MPF.14.0" DisplayName="Visual Studio MPF 14.0" d:Source="Installed" Version="[14.0]" />

gets the build message:

• Could not find schema information for the attribute 'http://schemas.microsoft.com/developer/vsx-schema-design/2011:Source'.

and

<Asset Type="Microsoft.VisualStudio.VsPackage" d:Source="Project" d:ProjectName="%CurrentProject%" Path="|%CurrentProject%;PkgdefProjectOutputGroup|" />

gets the two build messages:

• Could not find schema information for the attribute 'http://schemas.microsoft.com/developer/vsx-schema-design/2011:Source'.
• Could not find schema information for the attribute 'http://schemas.microsoft.com/developer/vsx-schema-design/2011:ProjectName'.

I used the VSIX Project template to generate the project.

Thanks.