title: How do we trigger a build only for tags matching a pattern
body: <p>I want to create a build script specifically when I push a tag pattern on git (not a branch).</p>
  
  <p>But I cannot find it in the </p>
  
  <ul>
  <li><a href="https://docs.microsoft.com/en-us/azure/devops/pipelines/process/expressions?view=vsts" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/devops/pipelines/process/expressions?view=vsts</a></li>
  <li><a href="https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=vsts&amp;tabs=yaml%2Cbatch" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=vsts&amp;tabs=yaml%2Cbatch</a></li>
  <li><a href="https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=vsts" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=vsts</a></li>
  </ul>
  
  <p>I'm looking specifically at "pattern" rather than a static string</p>