Very confused around creating a nuspec file with specific targets - nuget

Question

I have a nuspec file with the following structure
<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
<metadata>
<id>XLabs.Forms</id>
<version>2.2.0-pre05</version>
<title>XLabs - Forms</title>
<authors>XLabs Team</authors>
<owners>XLabs Team</owners>
<licenseUrl>https://github.com/XLabs/Xamarin-Forms-Labs/blob/master/LICENSE</licenseUrl>
<projectUrl>https://github.com/XLabs/Xamarin-Forms-Labs</projectUrl>
<iconUrl>https://raw.githubusercontent.com/XLabs/Xamarin-Forms-Labs/master/Design/Icons/nuget/icon_nuget.png</iconUrl>
<requireLicenseAcceptance>false</requireLicenseAcceptance>
<description>This package contains the cross-platform XLabs Forms framework and controls.</description>
<summary>XLabs is a open source project that aims to provide a powerfull and cross platform set of controls tailored to work with Xamarin Forms.</summary>
<releaseNotes>Updated for Xamarin Forms 2.2</releaseNotes>
<copyright>Copyright © 2016 XLabs Team</copyright>
<tags>Xamarin XLabs Forms Controls GridView ListView</tags>
<dependencies>
<group>
<dependency id="XLabs.Platform" version="[2.2.0-pre05]" />
<dependency id="Xamarin.Forms" version="2.2.0.31" />
</group>
</dependencies>
</metadata>
<files>
<!-- Assemblies: Android -->
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.dll" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.pdb" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms.Droid\bin\$configuration$\XLabs.Forms.Droid.dll" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms.Droid\bin\$configuration$\XLabs.Forms.Droid.pdb" target="lib\monoandroid" />
<!-- Assemblies: iOS -->
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.dll" target="lib\Xamarin.iOS10" />
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.pdb" target="lib\Xamarin.iOS10" />
<file src="..\..\source\Forms\XLabs.Forms.iOS\bin\$configuration$\XLabs.Forms.iOS.pdb" target="lib\Xamarin.iOS10" />
<file src="..\..\source\Forms\XLabs.Forms.iOS\bin\$configuration$\XLabs.Forms.iOS.dll" target="lib\Xamarin.iOS10" />
</files>
</package>
and it is driving me a little crazy :) The nupkg file that is created with this nuspec should ONLY install in a Xamarin iOS or base Xamarin Android project right? Not true, it is installing in any type of project (PCL, Windows 10, Windows 8, etc). I am at the point where I am not sure what else to do to limit the package so that it can only be installed in the targets that I need.
Can anyone see what I might be doing wrong?
UPDATE: Here is the latest version of the nuspec file that I have tried that still DOES NOT work. The following will create a package that installed in a Windows 8, Windows Mobile, and PCL project even though it only contains Android bases assemblies
<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
<metadata>
<id>XLabs.Forms</id>
<version>2.2.0-pre05</version>
<title>XLabs - Forms</title>
<authors>XLabs Team</authors>
<owners>XLabs Team</owners>
<licenseUrl>https://github.com/XLabs/Xamarin-Forms-Labs/blob/master/LICENSE</licenseUrl>
<projectUrl>https://github.com/XLabs/Xamarin-Forms-Labs</projectUrl>
<iconUrl>https://raw.githubusercontent.com/XLabs/Xamarin-Forms-Labs/master/Design/Icons/nuget/icon_nuget.png</iconUrl>
<requireLicenseAcceptance>false</requireLicenseAcceptance>
<description>This package contains the cross-platform XLabs Forms framework and controls.</description>
<summary>XLabs is a open source project that aims to provide a powerfull and cross platform set of controls tailored to work with Xamarin Forms.</summary>
<releaseNotes>Updated for Xamarin Forms 2.2</releaseNotes>
<copyright>Copyright © 2016 XLabs Team</copyright>
<tags>Xamarin XLabs Forms Controls GridView ListView</tags>
<dependencies>
<group targetFramework="monoandroid">
<dependency id="XLabs.Core" version="[2.2.0-pre05]" />
<dependency id="XLabs.IoC" version="[2.2.0-pre05]" />
<dependency id="XLabs.Platform" version="[2.2.0-pre05]" />
<dependency id="XLabs.Serialization" version="[2.2.0-pre05]" />
<dependency id="Xamarin.Forms" version="2.2.0.31" />
</group>
</dependencies>
</metadata>
<files>
<!-- Content Files -->
<file src="..\..\docs\XLabs.Forms.Readme.md" target="content\XLabs.Forms.Readme.md" />
<!-- Assemblies: Android -->
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.dll" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms\bin\$configuration$\XLabs.Forms.pdb" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms.Droid\bin\$configuration$\XLabs.Forms.Droid.dll" target="lib\monoandroid" />
<file src="..\..\source\Forms\XLabs.Forms.Droid\bin\$configuration$\XLabs.Forms.Droid.pdb" target="lib\monoandroid" />
</files>
</package>

Answer 1

I believe it is because you have a group dependency that does not have a target framework. The group dependency will cause NuGet to install the Xamarin.Forms and XLabs.Platform NuGet packages whilst the assemblies in your lib directories would not be used unless you are installing into an iOS or Android project.
I would try adding a target framework for iOS and Android.
<group targetFramework="Xamarin.iOS10">
<dependency id="XLabs.Platform" version="[2.2.0-pre05]" />
<dependency id="Xamarin.Forms" version="2.2.0.31" />
</group>
<group targetFramework="MonoAndroid">
<dependency id="XLabs.Platform" version="[2.2.0-pre05]" />
<dependency id="Xamarin.Forms" version="2.2.0.31" />
</group>

Answer 2

Turns out the issue was with this line
<!-- Content Files -->
<file src="..\..\docs\XLabs.Forms.Readme.md" target="content\XLabs.Forms.Readme.md" />
Since that doesn't have a target moniker in it, it is valid for ALL target frameworks. Once I removed that, everything started working. I think the nuspec file format needs a LOT more details in its documentation :)