title: how is the properties set in this pom.xml?
body: <p>This is the snippet of <code>pom.xml</code> from my project.</p>
  
  <pre><code>&lt;properties&gt;
          &lt;Port&gt;2020&lt;/Port&gt;   
          &lt;threads&gt;20&lt;/threads&gt;
          &lt;test.suite /&gt;
          &lt;test.suite.path /&gt;
          &lt;useTag /&gt;
          &lt;useTestCase /&gt;
          &lt;args&gt;-Dthreads=${threads} -Dtest.suite.path=${test.suite.path} -Dappenv=${test.app.env} -Dtest.suite=${test.suite} -DuseTag=${useTag} -DuseTestCase=${useTestCase}&lt;/args&gt;
      &lt;/properties&gt;
  </code></pre>
  
  <p>when maven build is made, I am wondering how the variables <code>test.suite</code>, <code>test.suite.path</code>, <code>useTestCase</code> are set? I do not see it anywhere in the <code>pom</code>. but the <code>Jenkins</code> build is working fine and it has substituted values for these placeholders.</p>
  
  <p>what is the use of using this kind of property setting. <code>&lt;variable/&gt;</code> rather than <code>&lt;variable&gt;...&lt;/variable&gt;</code> ?</p>