code: public SpringApplicationBuilder sibling(Class<?>[] sources, String... args) {
  		return runAndExtractParent(args).child(sources);
  	}
docs: Create a sibling application (one with the same parent). A side effect of calling
  this method is that the current application (and its parent) are started if they
  are not already running.
  @param sources the sources for the application (Spring configuration)
  @param args the command line arguments to use when starting the current app and its
  parent
  @return the new sibling builder