title: Gradle's withType usage
body: <p>Like <a href="https://stackoverflow.com/questions/45880994/where-are-the-docs-for-tasks-withtype">this other user</a>, I have problems to understand the <code>withType</code> usage, example</p>
  
  <pre><code>tasks.withType(JavaCompile) {
      options.compilerArgs.add("-Xbootclasspath/p:${file}")
  }
  </code></pre>
  
  <p>... and differently from him, I have found official docs, as always, completely unuseful. Can you tell me what <code>withType</code> exactly does?</p>