title: How to add a custom Property as a child of a PropertyGroup in MSBuild?
body: <p>I have the following build script, which I run with MSBuild:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;Project DefaultTargets="Compile" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion ="3.5"&gt;
  &lt;PropertyGroup&gt;
      &lt;BuildDir Condition=" '$(BuildDir)'==' ' "&gt;$(BaseDir)/build&lt;/BuildDir&gt;
      &lt;ProdDir &gt;$(BuildDir)/prod&lt;/ProdDir&gt;
      &lt;TestDir&gt;$(BuildDir)/test&lt;/TestDir&gt;
      &lt;MMC2SourceDir&gt;SteuerungsZugriffTest/mmc2&lt;/MMC2SourceDir&gt;
      &lt;UserSourceDir&gt;SteuerungsZugriffTest/user&lt;/UserSourceDir&gt;
      &lt;TestXMLDir&gt;$(BuildDir)/test-results&lt;/TestXMLDir&gt;
      &lt;SolutionFile Condition=" '$(SolutionFile)'==' ' "&gt;HMI2.0.sln&lt;/SolutionFile&gt;"
      &lt;NUnitTest&gt;nunit-console.exe&lt;/NUnitTest&gt;
  &lt;/PropertyGroup&gt;
  &lt;Target Name="Prepare"&gt;
      &lt;Message Text="Prepare everything" /&gt;
      &lt;MakeDir Directories="$(BuildDir)" /&gt;
      &lt;MakeDir Directories="$(ProdDir)" /&gt;
  &lt;/Target&gt;
  ...
  </code></pre>
  
  <p>When I now start script on the command line:</p>
  
  <pre><code>D:\MyDir&gt;msbuild /property:BaseDir=D:\MyDir MyScript.build
  </code></pre>
  
  <p>I got the following error on the commandline output:</p>
  
  <pre><code>D:\MyDir&gt;MyScript.build(11,78): error MSB4067: Das &lt;#text&gt;-Element unterhalb des &lt;PropertyGroup&gt;-Elements ist unbekannt.
  </code></pre>
  
  <p>Which basically means: <em>The element&lt;#text> is an unknown child</em>.</p>
  
  <p>Does anybody have an idea?</p>
  
  <p>Edit: Sorry, I completed now the script</p>