<AllowUnsafeBlocks>true</AllowUnsafeBlocks>

unsafe-netstandard1.3.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>net451</TargetFrameworks>
    <!-- <TargetFrameworks>netstandard2.0;netstandard1.3;net451</TargetFrameworks> -->
    <EnableDefaultCompileItems>true</EnableDefaultCompileItems>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>

    <VersionPrefix>1.0.0</VersionPrefix>
    <VersionSuffix>alpha</VersionSuffix>
    <AssemblyName>UString</AssemblyName>
    <PackageId>UString</PackageId>
    <NetStandardImplicitPackageVersion>1.6.0</NetStandardImplicitPackageVersion>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>  
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="System.ValueTuple" Version="4.3.0" />
    <PackageReference Include="runtime.win7-x86.Microsoft.NETCore.Runtime.CoreCLR" Version="1.0.1" />
    <!--      <PackageReference Include="System.Private.CoreLib     -->
  </ItemGroup>
  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.3' ">
    <PackageReference Include="System.Xml.XDocument" Version="4.3.0" />
  </ItemGroup>
  <ItemGroup Condition=" '$(TargetFramework)' == 'net451' ">
    <Reference Include="System.ServiceModel" />
    <Reference Include="System.Xml" />
    <Reference Include="System.Xml.Linq" />
    <Reference Include="System" />
    <Reference Include="Microsoft.CSharp" />
  </ItemGroup>