diff --git a/src/Pure/Admin/build_doc.scala b/src/Pure/Admin/build_doc.scala
--- a/src/Pure/Admin/build_doc.scala
+++ b/src/Pure/Admin/build_doc.scala
@@ -1,124 +1,124 @@
 /*  Title:      Pure/Admin/build_doc.scala
     Author:     Makarius
 
 Build Isabelle documentation.
 */
 
 package isabelle
 
 
 object Build_Doc {
   /* build_doc */
 
   def build_doc(
     options: Options,
     progress: Progress = new Progress,
     all_docs: Boolean = false,
     max_jobs: Int = 1,
     sequential: Boolean = false,
     docs: List[String] = Nil,
     view: Boolean = false
   ): Unit = {
     val sessions_structure = Sessions.load_structure(options)
     val selected =
       for {
         session <- sessions_structure.build_topological_order
         info = sessions_structure(session)
         if info.groups.contains("doc")
         doc = info.options.string("document_variants")
         if all_docs || docs.contains(doc)
       } yield (doc, session)
 
     val documents = selected.map(_._1)
     val selection = Sessions.Selection(sessions = selected.map(_._2))
 
     docs.filter(doc => !documents.contains(doc)) match {
       case Nil =>
       case bad => error("No documentation session for " + commas_quote(bad))
     }
 
     progress.echo("Build started for sessions " + commas_quote(selection.sessions))
     val build_results =
       Build.build(options, selection = selection, progress = progress, max_jobs = max_jobs)
     if (!build_results.ok) error("Build failed")
 
     progress.echo("Build started for documentation " + commas_quote(documents))
     val doc_options = options + "document=pdf"
     val deps = Sessions.load_structure(doc_options).selection_deps(selection)
 
     val errs =
       Par_List.map[(String, String), Option[String]](
       {
         case (doc, session) =>
           try {
             progress.expose_interrupt()
             progress.echo("Documentation " + quote(doc) + " ...")
 
             using(Export.open_session_context(build_results.store, deps.base_info(session))) {
               session_context =>
                 Document_Build.build_documents(
                   Document_Build.context(session_context),
                   output_pdf = Some(Path.explode("~~/doc")))
             }
             None
           }
           catch {
             case Exn.Interrupt.ERROR(msg) =>
               val sep = if (msg.contains('\n')) "\n" else " "
               Some("Documentation " + quote(doc) + " failed:" + sep + msg)
           }
       }, selected, sequential = sequential).flatten
 
     if (errs.nonEmpty) error(cat_lines(errs))
 
     if (view) {
       for (doc <- Doc.main_contents().docs if docs.contains(doc.name)) {
         Doc.view(doc.path)
       }
     }
   }
 
 
   /* Isabelle tool wrapper */
 
   val isabelle_tool =
     Isabelle_Tool("build_doc", "build Isabelle documentation", Scala_Project.here,
       { args =>
         var view = false
         var all_docs = false
         var max_jobs = 1
         var sequential = false
         var options = Options.init()
 
         val getopts =
           Getopts("""
 Usage: isabelle build_doc [OPTIONS] [DOCS ...]
 
   Options are:
-    -V           view resulting documents
+    -V           view explicitly given documents
     -a           select all documentation sessions
     -j INT       maximum number of parallel jobs (default 1)
     -o OPTION    override Isabelle system OPTION (via NAME=VAL or NAME)
     -s           sequential LaTeX jobs
 
   Build Isabelle documentation from documentation sessions with
   suitable document_variants entry.
 """,
             "V" -> (_ => view = true),
             "a" -> (_ => all_docs = true),
             "j:" -> (arg => max_jobs = Value.Int.parse(arg)),
             "o:" -> (arg => options = options + arg),
             "s" -> (_ => sequential = true))
 
         val docs = getopts(args)
 
         if (!all_docs && docs.isEmpty) getopts.usage()
 
         val progress = new Console_Progress()
 
         progress.interrupt_handler {
           build_doc(options, progress = progress, all_docs = all_docs, max_jobs = max_jobs,
             sequential = sequential, docs = docs, view = view)
         }
       })
 }