HasTrailingSlash in MSBuild scripts

There is useful undocumented function that may be used in MSBuild scripts conditions, called HasTrailingSlash. As its name implies, the function checks its only argument for trailing backward slash:

Sample updated at 01-Fev-2008 (recently somebody complained that while function works my old sample does not :):

<!-- Initial target will be always called first to verify properties -->
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
InitialTargets="VerifyInputParameters">

    <!-- Target verifies that the property is not empty (throws error) -->
    <!-- and has trailing slash (adds one if no slash provided)        -->
    <Target Name="VerifyInputParameters">

        <Error Condition="'$(ExternalPath)' == ''" Text="ExternalPath is empty" />

        <CreateProperty Condition="!HasTrailingSlash('$(ExternalPath)')" 
        Value="$(ExternalPath)\">

              <Output TaskParameter="Value" PropertyName="ExternalPath" />

        </CreateProperty>

    </Target>

    <!-- Here goes the rest of the project -->

</Project>

<PropertyGroup>

 <OutputPath Condition=" !HasTrailingSlash('$(OutputPath)') ">

  $(OutputPath)\

 </OutputPath>

</PropertyGroup>

The thing is, the function is used extensively in Microsoft system targets files (for example, in Microsoft.TeamFoundation.Build.targets file) and still does not appear in MSBuild documentation. Beats me...

See also new TFSBuild site for more details.