Better documentation of getSubProjectExecutor()

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@761528 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/Executor.java

@@ -35,6 +35,12 @@ public interface Executor {
 
     /**
      * Get the appropriate subproject Executor instance.
+     *
+     * This allows the top executor to control what type of executor is used to execute
+     * subprojects via <ant>/<antcall>/<subant> and task that extend these.
+     * All bundled Executors return a SingleCheckExecutor (running a merged set of
+     * depended targets for all targets called) to run sub-builds.
+     *
      * @return an Executor instance.
      */
     Executor getSubProjectExecutor();