Minor comment and wording updates

core/src/main/scala/org/apache/spark/deploy/SparkSubmitArguments.scala

@@ -438,7 +438,7 @@ private[spark] class SparkSubmitArguments(args: Seq[String], env: Map[String, St
       outStream.println("Unknown/unsupported param " + unknownParam)
     }
     outStream.println(
-      """Usage: spark-submit [options] <app jar | python file> [app options]
+      """Usage: spark-submit [options] <app jar | python file> [app arguments]
         |Options:
         |  --master MASTER_URL         spark://host:port, mesos://host:port, yarn, or local.
         |  --deploy-mode DEPLOY_MODE   Whether to launch the driver program locally ("client") or

core/src/main/scala/org/apache/spark/deploy/master/ui/MasterPage.scala

@@ -46,19 +46,19 @@ private[spark] class MasterPage(parent: MasterWebUI) extends WebUIPage("") {
     val stateFuture = (master ? RequestMasterState)(timeout).mapTo[MasterStateResponse]
     val state = Await.result(stateFuture, timeout)
 
-    val workerHeaders = Seq("Id", "Address", "State", "Cores", "Memory")
+    val workerHeaders = Seq("Worker Id", "Address", "State", "Cores", "Memory")
     val workers = state.workers.sortBy(_.id)
     val workerTable = UIUtils.listingTable(workerHeaders, workerRow, workers)
 
-    val appHeaders = Seq("ID", "Name", "Cores", "Memory per Node", "Submitted Time", "User",
-      "State", "Duration")
+    val appHeaders = Seq("Application ID", "Name", "Cores", "Memory per Node", "Submitted Time",
+      "User", "State", "Duration")
     val activeApps = state.activeApps.sortBy(_.startTime).reverse
     val activeAppsTable = UIUtils.listingTable(appHeaders, appRow, activeApps)
     val completedApps = state.completedApps.sortBy(_.endTime).reverse
     val completedAppsTable = UIUtils.listingTable(appHeaders, appRow, completedApps)
 
-    val driverHeaders = Seq("ID", "Submitted Time", "Worker", "State", "Cores", "Memory",
-      "Main Class")
+    val driverHeaders = Seq("Submission ID", "Submitted Time", "Worker", "State", "Cores",
+      "Memory", "Main Class")
     val activeDrivers = state.activeDrivers.sortBy(_.startTime).reverse
     val activeDriversTable = UIUtils.listingTable(driverHeaders, driverRow, activeDrivers)
     val completedDrivers = state.completedDrivers.sortBy(_.startTime).reverse
@@ -77,7 +77,7 @@ private[spark] class MasterPage(parent: MasterWebUI) extends WebUIPage("") {
                 state.restUri.map { uri =>
                   <li>
                     <strong>REST URL:</strong> {uri}
-                    <span class="rest-uri"> (for standalone cluster mode in Spark 1.3+)</span>
+                    <span class="rest-uri"> (cluster mode)</span>
                   </li>
                 }.getOrElse { Seq.empty }
               }

core/src/main/scala/org/apache/spark/deploy/rest/StandaloneRestClient.scala

@@ -31,19 +31,24 @@ import org.apache.spark.{Logging, SparkConf, SPARK_VERSION => sparkVersion}
  * This client is intended to communicate with the [[StandaloneRestServer]] and is
  * currently used for cluster mode only.
  *
- * The specific request sent to the server depends on the action as follows:
+ * In protocol version v1, the REST URL takes the form http://[host:port]/v1/submissions/[action],
+ * where [action] can be one of create, kill, or status. Each type of request is represented in
+ * an HTTP message sent to the following prefixes:
  *   (1) submit - POST to /submissions/create
  *   (2) kill - POST /submissions/kill/[submissionId]
  *   (3) status - GET /submissions/status/[submissionId]
  *
  * In the case of (1), parameters are posted in the HTTP body in the form of JSON fields.
  * Otherwise, the URL fully specifies the intended action of the client.
  *
- * Additionally, the base URL includes the version of the protocol. For instance:
- * http://1.2.3.4:6066/v1/submissions/create. Since the protocol is expected to be stable
- * across Spark versions, existing fields cannot be added or removed. In the rare event that
- * forward or backward compatibility is broken, Spark must introduce a new protocol version
- * (e.g. v2). The client and the server must communicate on the same version of the protocol.
+ * Since the protocol is expected to be stable across Spark versions, existing fields cannot be
+ * added or removed, though new optional fields can be added. In the rare event that forward or
+ * backward compatibility is broken, Spark must introduce a new protocol version (e.g. v2).
+ *
+ * The client and the server must communicate using the same version of the protocol. If there
+ * is a mismatch, the server will respond with the highest protocol version it supports. A future
+ * implementation of this client can use that information to retry using the version specified
+ * by the server.
  */
 private[spark] class StandaloneRestClient extends Logging {
   import StandaloneRestClient._