MSBuild .target files and MSBuild Task libraries

Gentoo Mono Handbook
 
MSBuildExtensionsPath
This location is a useful place to put custom target files.
What is it's value on gentoo? Where it is defined?
MSBuildToolsPath
The installation path of the MSBuild version that's associated with the value of MSBuildToolsVersion. This property cannot be overridden. You can modify the value of MSBuildToolsPath by defining a custom Toolset.
MSBuildBinPath
The absolute path of the folder where the MSBuild binaries that are currently being used are located
MSBuildProjectDirectory
The absolute path of the directory where the project file is located
Do not include the final backslash on these properties1

MSBuildExtensionsPath

http://freebsd.polarhome.com/service/man/?qf=xbuild&tf=2&of=OpenSuSE&sf=1 MSBuild extensions are usually installed in $(MSBuildExtensionтАР sPath), which xbuild resolves to $prefix/lib/mono/xbuild . When used in Import, like: <Import Project="$(MSBuildExtensionsPath)\TestTargets.tarтАР gets"/> xbuild tries various values for the msbuild property $(MSBuildExtensionsPath), in order: 1. Paths specified in the environment variable $MSBuildExtenтАР sionsPath. 2. /Library/Frameworks/Mono.framework/External/xbuild on Mac OSX. 3. $XDG_CONFIG_HOME/xbuild/tasks (or Environment.SpecialтАР Folder.ApplicationData) 4. $prefix/lib/mono/xbuild (default location) Anywhere else in the project files, $(MSBuildExtensionsPath) will always resolve to the default location. This is a xbuild- only feature. This is also applicable for the properties $(MSBuildExtensionsPath32) and $(MSBuildExtensionsPath64), and the environment variables have the corresponding names - MSBuildExtensionsPath32/64 .
<PropertyGroup Condition="Exists('/usr/lib64/mono/msbuildtasks/MSBuild.Community.Tasks.dll')">
    <MSBuildCommunityTasksPath>/usr/lib64/mono/msbuildtasks</MSBuildCommunityTasksPath>
    <MSBuildCommunityTasksLib>$(MSBuildCommunityTasksPath)/MSBuild.Community.Tasks.dll</MSBuildCommunityTasksLib>
</PropertyGroup>


https://gitweb.gentoo.org/proj/dotnet.git/diff/?h=dotnet-2010
<importTargets Condition="$(devel)">$(binDir)\MSBuild.Community.Tasks.Targets</importTargets>
<importTargets Condition="!$(devel)">$(MSBuildExtensionsPath)\MSBuildCommunityTasks\MSBuild.Community.Tasks.Targets</importTargets>
https://github.com/gentoo/dotnet/blob/118bf4f185f884cec522c066dd148df870897961/dev-dotnet/msbuildtasks/msbuildtasks-1.5.0.196.ebuild
/usr/lib/mono/4.5/MSBuild.Community.Tasks.Targets

MSBuild Toolset (ToolsVersion)
    "Only that Toolset property (or $(MSBuildBinPath)), is required."
Standard and Custom Toolset Configurations
MSBuild Reserved and Well-Known Properties