diff --git a/src/Pure/PIDE/markup.scala b/src/Pure/PIDE/markup.scala
--- a/src/Pure/PIDE/markup.scala
+++ b/src/Pure/PIDE/markup.scala
@@ -1,714 +1,716 @@
 /*  Title:      Pure/PIDE/markup.scala
     Author:     Makarius
 
 Quasi-abstract markup elements.
 */
 
 package isabelle
 
 
 object Markup
 {
   /* elements */
 
   object Elements
   {
     def apply(elems: Set[String]): Elements = new Elements(elems)
     def apply(elems: String*): Elements = apply(Set(elems: _*))
     val empty: Elements = apply()
     val full: Elements =
       new Elements(Set.empty)
       {
         override def apply(elem: String): Boolean = true
         override def toString: String = "Elements.full"
       }
   }
 
   sealed class Elements private[Markup](private val rep: Set[String])
   {
     def apply(elem: String): Boolean = rep.contains(elem)
     def + (elem: String): Elements = new Elements(rep + elem)
     def ++ (elems: Elements): Elements = new Elements(rep ++ elems.rep)
     def - (elem: String): Elements = new Elements(rep - elem)
     def -- (elems: Elements): Elements = new Elements(rep -- elems.rep)
     override def toString: String = rep.mkString("Elements(", ",", ")")
   }
 
 
   /* properties */
 
   val NAME = "name"
   val Name = new Properties.String(NAME)
 
   val XNAME = "xname"
   val XName = new Properties.String(XNAME)
 
   val KIND = "kind"
   val Kind = new Properties.String(KIND)
 
   val CONTENT = "content"
   val Content = new Properties.String(CONTENT)
 
   val SERIAL = "serial"
   val Serial = new Properties.Long(SERIAL)
 
   val INSTANCE = "instance"
   val Instance = new Properties.String(INSTANCE)
 
 
   /* basic markup */
 
   val Empty: Markup = Markup("", Nil)
   val Broken: Markup = Markup("broken", Nil)
 
   class Markup_String(val name: String, prop: String)
   {
     private val Prop = new Properties.String(prop)
 
     def apply(s: String): Markup = Markup(name, Prop(s))
     def unapply(markup: Markup): Option[String] =
       if (markup.name == name) Prop.unapply(markup.properties) else None
   }
 
   class Markup_Int(val name: String, prop: String)
   {
     private val Prop = new Properties.Int(prop)
 
     def apply(i: Int): Markup = Markup(name, Prop(i))
     def unapply(markup: Markup): Option[Int] =
       if (markup.name == name) Prop.unapply(markup.properties) else None
   }
 
   class Markup_Long(val name: String, prop: String)
   {
     private val Prop = new Properties.Long(prop)
 
     def apply(i: Long): Markup = Markup(name, Prop(i))
     def unapply(markup: Markup): Option[Long] =
       if (markup.name == name) Prop.unapply(markup.properties) else None
   }
 
 
   /* meta data */
 
   val META_TITLE = "meta_title"
   val META_CREATOR = "meta_creator"
   val META_CONTRIBUTOR = "meta_contributor"
   val META_DATE = "meta_date"
   val META_LICENSE = "meta_license"
   val META_DESCRIPTION = "meta_description"
 
 
   /* formal entities */
 
   val BINDING = "binding"
   val ENTITY = "entity"
 
   object Entity
   {
     val Def = new Properties.Long("def")
     val Ref = new Properties.Long("ref")
 
     def unapply(markup: Markup): Option[(String, String)] =
       markup match {
         case Markup(ENTITY, props) =>
           val kind = Kind.unapply(props).getOrElse("")
           val name = Name.unapply(props).getOrElse("")
           Some((kind, name))
         case _ => None
       }
   }
 
 
   /* completion */
 
   val COMPLETION = "completion"
   val NO_COMPLETION = "no_completion"
 
   val UPDATE = "update"
 
 
   /* position */
 
   val LINE = "line"
   val END_LINE = "line"
   val OFFSET = "offset"
   val END_OFFSET = "end_offset"
   val FILE = "file"
   val ID = "id"
 
   val DEF_LINE = "def_line"
   val DEF_OFFSET = "def_offset"
   val DEF_END_OFFSET = "def_end_offset"
   val DEF_FILE = "def_file"
   val DEF_ID = "def_id"
 
   val POSITION_PROPERTIES = Set(LINE, OFFSET, END_OFFSET, FILE, ID)
   def position_property(entry: Properties.Entry): Boolean = POSITION_PROPERTIES(entry._1)
 
   val POSITION = "position"
 
 
   /* expression */
 
   val EXPRESSION = "expression"
   object Expression
   {
     def unapply(markup: Markup): Option[String] =
       markup match {
         case Markup(EXPRESSION, Kind(kind)) => Some(kind)
         case Markup(EXPRESSION, _) => Some("")
         case _ => None
       }
   }
 
 
   /* citation */
 
   val CITATION = "citation"
   val Citation = new Markup_String(CITATION, NAME)
 
 
   /* embedded languages */
 
   val Symbols = new Properties.Boolean("symbols")
   val Antiquotes = new Properties.Boolean("antiquotes")
   val Delimited = new Properties.Boolean("delimited")
 
   val LANGUAGE = "language"
   object Language
   {
     val DOCUMENT = "document"
     val ML = "ML"
     val SML = "SML"
     val PATH = "path"
     val UNKNOWN = "unknown"
 
     def unapply(markup: Markup): Option[(String, Boolean, Boolean, Boolean)] =
       markup match {
         case Markup(LANGUAGE, props) =>
           (props, props, props, props) match {
             case (Name(name), Symbols(symbols), Antiquotes(antiquotes), Delimited(delimited)) =>
               Some((name, symbols, antiquotes, delimited))
             case _ => None
           }
         case _ => None
       }
   }
 
 
   /* external resources */
 
   val PATH = "path"
   val Path = new Markup_String(PATH, NAME)
 
   val EXPORT_PATH = "export_path"
   val Export_Path = new Markup_String(EXPORT_PATH, NAME)
 
   val URL = "url"
   val Url = new Markup_String(URL, NAME)
 
   val DOC = "doc"
   val Doc = new Markup_String(DOC, NAME)
 
 
   /* pretty printing */
 
   val Consistent = new Properties.Boolean("consistent")
   val Indent = new Properties.Int("indent")
   val Width = new Properties.Int("width")
 
   object Block
   {
     val name = "block"
     def apply(c: Boolean, i: Int): Markup =
       Markup(name,
         (if (c) Consistent(c) else Nil) :::
         (if (i != 0) Indent(i) else Nil))
     def unapply(markup: Markup): Option[(Boolean, Int)] =
       if (markup.name == name) {
         val c = Consistent.unapply(markup.properties).getOrElse(false)
         val i = Indent.unapply(markup.properties).getOrElse(0)
         Some((c, i))
       }
       else None
   }
 
   object Break
   {
     val name = "break"
     def apply(w: Int, i: Int): Markup =
       Markup(name,
         (if (w != 0) Width(w) else Nil) :::
         (if (i != 0) Indent(i) else Nil))
     def unapply(markup: Markup): Option[(Int, Int)] =
       if (markup.name == name) {
         val w = Width.unapply(markup.properties).getOrElse(0)
         val i = Indent.unapply(markup.properties).getOrElse(0)
         Some((w, i))
       }
       else None
   }
 
   val ITEM = "item"
   val BULLET = "bullet"
 
   val SEPARATOR = "separator"
 
 
   /* text properties */
 
   val WORDS = "words"
 
   val HIDDEN = "hidden"
 
   val DELETE = "delete"
 
 
   /* misc entities */
 
   val THEORY = "theory"
   val CLASS = "class"
   val TYPE_NAME = "type_name"
   val FIXED = "fixed"
   val CASE = "case"
   val CONSTANT = "constant"
   val DYNAMIC_FACT = "dynamic_fact"
 
 
   /* inner syntax */
 
   val TFREE = "tfree"
   val TVAR = "tvar"
   val FREE = "free"
   val SKOLEM = "skolem"
   val BOUND = "bound"
   val VAR = "var"
   val NUMERAL = "numeral"
   val LITERAL = "literal"
   val DELIMITER = "delimiter"
   val INNER_STRING = "inner_string"
   val INNER_CARTOUCHE = "inner_cartouche"
 
   val TOKEN_RANGE = "token_range"
 
   val SORTING = "sorting"
   val TYPING = "typing"
   val CLASS_PARAMETER = "class_parameter"
 
   val ATTRIBUTE = "attribute"
   val METHOD = "method"
 
 
   /* antiquotations */
 
   val ANTIQUOTED = "antiquoted"
   val ANTIQUOTE = "antiquote"
 
   val ML_ANTIQUOTATION = "ML_antiquotation"
   val DOCUMENT_ANTIQUOTATION = "document_antiquotation"
   val DOCUMENT_ANTIQUOTATION_OPTION = "document_antiquotation_option"
 
 
   /* document text */
 
   val RAW_TEXT = "raw_text"
   val PLAIN_TEXT = "plain_text"
 
   val PARAGRAPH = "paragraph"
   val TEXT_FOLD = "text_fold"
 
   object Document_Tag
   {
     val ELEMENT = "document_tag"
     val IMPORTANT = "important"
     val UNIMPORTANT = "unimportant"
 
     def unapply(markup: Markup): Option[String] =
       markup match {
         case Markup(ELEMENT, Name(name)) => Some(name)
         case _ => None
       }
   }
 
 
   /* Markdown document structure */
 
   val MARKDOWN_PARAGRAPH = "markdown_paragraph"
   val MARKDOWN_ITEM = "markdown_item"
   val Markdown_Bullet = new Markup_Int("markdown_bullet", "depth")
   val Markdown_List = new Markup_String("markdown_list", "kind")
 
   val ITEMIZE = "itemize"
   val ENUMERATE = "enumerate"
   val DESCRIPTION = "description"
 
 
   /* ML */
 
   val ML_KEYWORD1 = "ML_keyword1"
   val ML_KEYWORD2 = "ML_keyword2"
   val ML_KEYWORD3 = "ML_keyword3"
   val ML_DELIMITER = "ML_delimiter"
   val ML_TVAR = "ML_tvar"
   val ML_NUMERAL = "ML_numeral"
   val ML_CHAR = "ML_char"
   val ML_STRING = "ML_string"
   val ML_COMMENT = "ML_comment"
 
   val ML_DEF = "ML_def"
   val ML_OPEN = "ML_open"
   val ML_STRUCTURE = "ML_structure"
   val ML_TYPING = "ML_typing"
 
   val ML_BREAKPOINT = "ML_breakpoint"
 
 
   /* outer syntax */
 
   val COMMAND = "command"
   val KEYWORD = "keyword"
   val KEYWORD1 = "keyword1"
   val KEYWORD2 = "keyword2"
   val KEYWORD3 = "keyword3"
   val QUASI_KEYWORD = "quasi_keyword"
   val IMPROPER = "improper"
   val OPERATOR = "operator"
   val STRING = "string"
   val ALT_STRING = "alt_string"
   val VERBATIM = "verbatim"
   val CARTOUCHE = "cartouche"
   val COMMENT = "comment"
 
+  val LOAD_COMMAND = "load_command"
+
 
   /* comments */
 
   val COMMENT1 = "comment1"
   val COMMENT2 = "comment2"
   val COMMENT3 = "comment3"
 
 
   /* timing */
 
   val Elapsed = new Properties.Double("elapsed")
   val CPU = new Properties.Double("cpu")
   val GC = new Properties.Double("gc")
 
   object Timing_Properties
   {
     def apply(timing: isabelle.Timing): Properties.T =
       Elapsed(timing.elapsed.seconds) ::: CPU(timing.cpu.seconds) ::: GC(timing.gc.seconds)
 
     def unapply(props: Properties.T): Option[isabelle.Timing] =
       (props, props, props) match {
         case (Elapsed(elapsed), CPU(cpu), GC(gc)) =>
           Some(new isabelle.Timing(Time.seconds(elapsed), Time.seconds(cpu), Time.seconds(gc)))
         case _ => None
       }
 
     def parse(props: Properties.T): isabelle.Timing =
       unapply(props) getOrElse isabelle.Timing.zero
   }
 
   val TIMING = "timing"
 
   object Timing
   {
     def apply(timing: isabelle.Timing): Markup = Markup(TIMING, Timing_Properties(timing))
 
     def unapply(markup: Markup): Option[isabelle.Timing] =
       markup match {
         case Markup(TIMING, Timing_Properties(timing)) => Some(timing)
         case _ => None
       }
   }
 
 
   /* process result */
 
   val Return_Code = new Properties.Int("return_code")
 
   object Process_Result
   {
     def apply(result: Process_Result): Properties.T =
       Return_Code(result.rc) :::
         (if (result.timing.is_zero) Nil else Timing_Properties(result.timing))
 
     def unapply(props: Properties.T): Option[Process_Result] =
       props match {
         case Return_Code(rc) =>
           val timing = Timing_Properties.unapply(props).getOrElse(isabelle.Timing.zero)
           Some(isabelle.Process_Result(rc, timing = timing))
         case _ => None
       }
   }
 
 
   /* command indentation */
 
   object Command_Indent
   {
     val name = "command_indent"
     def unapply(markup: Markup): Option[Int] =
       if (markup.name == name) Indent.unapply(markup.properties) else None
   }
 
 
   /* goals */
 
   val GOAL = "goal"
   val SUBGOAL = "subgoal"
 
 
   /* command status */
 
   val TASK = "task"
 
   val ACCEPTED = "accepted"
   val FORKED = "forked"
   val JOINED = "joined"
   val RUNNING = "running"
   val FINISHED = "finished"
   val FAILED = "failed"
   val CANCELED = "canceled"
   val INITIALIZED = "initialized"
   val FINALIZED = "finalized"
   val CONSOLIDATING = "consolidating"
   val CONSOLIDATED = "consolidated"
 
 
   /* interactive documents */
 
   val VERSION = "version"
   val ASSIGN = "assign"
 
 
   /* prover process */
 
   val PROVER_COMMAND = "prover_command"
   val PROVER_ARG = "prover_arg"
 
 
   /* messages */
 
   val INIT = "init"
   val STATUS = "status"
   val REPORT = "report"
   val RESULT = "result"
   val WRITELN = "writeln"
   val STATE = "state"
   val INFORMATION = "information"
   val TRACING = "tracing"
   val WARNING = "warning"
   val LEGACY = "legacy"
   val ERROR = "error"
   val NODES_STATUS = "nodes_status"
   val PROTOCOL = "protocol"
   val SYSTEM = "system"
   val STDOUT = "stdout"
   val STDERR = "stderr"
   val EXIT = "exit"
 
   val WRITELN_MESSAGE = "writeln_message"
   val STATE_MESSAGE = "state_message"
   val INFORMATION_MESSAGE = "information_message"
   val TRACING_MESSAGE = "tracing_message"
   val WARNING_MESSAGE = "warning_message"
   val LEGACY_MESSAGE = "legacy_message"
   val ERROR_MESSAGE = "error_message"
 
   val messages = Map(
     WRITELN -> WRITELN_MESSAGE,
     STATE -> STATE_MESSAGE,
     INFORMATION -> INFORMATION_MESSAGE,
     TRACING -> TRACING_MESSAGE,
     WARNING -> WARNING_MESSAGE,
     LEGACY -> LEGACY_MESSAGE,
     ERROR -> ERROR_MESSAGE)
 
   val message: String => String = messages.withDefault((s: String) => s)
 
   val NO_REPORT = "no_report"
 
   val BAD = "bad"
 
   val INTENSIFY = "intensify"
 
 
   /* active areas */
 
   val BROWSER = "browser"
   val GRAPHVIEW = "graphview"
   val THEORY_EXPORTS = "theory_exports"
 
   val SENDBACK = "sendback"
   val PADDING = "padding"
   val PADDING_LINE = (PADDING, "line")
   val PADDING_COMMAND = (PADDING, "command")
 
   val DIALOG = "dialog"
   val Result = new Properties.String(RESULT)
 
   val JEDIT_ACTION = "jedit_action"
 
 
   /* protocol message functions */
 
   val FUNCTION = "function"
 
   class Function(val name: String)
   {
     val PROPERTY: Properties.Entry = (FUNCTION, name)
   }
 
   class Properties_Function(name: String) extends Function(name)
   {
     def unapply(props: Properties.T): Option[Properties.T] =
       props match {
         case PROPERTY :: args => Some(args)
         case _ => None
       }
   }
 
   class Name_Function(name: String) extends Function(name)
   {
     def unapply(props: Properties.T): Option[String] =
       props match {
         case List(PROPERTY, (NAME, a)) => Some(a)
         case _ => None
       }
   }
 
   object ML_Statistics extends Function("ML_statistics")
   {
     def unapply(props: Properties.T): Option[(Long, String)] =
       props match {
         case List(PROPERTY, ("pid", Value.Long(pid)), ("stats_dir", stats_dir)) =>
           Some((pid, stats_dir))
         case _ => None
       }
   }
 
   val command_timing_properties: Set[String] = Set(FILE, OFFSET, NAME, Elapsed.name)
   def command_timing_property(entry: Properties.Entry): Boolean = command_timing_properties(entry._1)
 
   object Command_Timing extends Properties_Function("command_timing")
   object Theory_Timing extends Properties_Function("theory_timing")
   object Session_Timing extends Properties_Function("session_timing")
   {
     val Threads = new Properties.Int("threads")
   }
   object Task_Statistics extends Properties_Function("task_statistics")
 
   object Loading_Theory extends Properties_Function("loading_theory")
   object Finished_Theory extends Name_Function("finished_theory")
   object Build_Session_Finished extends Function("build_session_finished")
 
   object Commands_Accepted extends Function("commands_accepted")
   object Assign_Update extends Function("assign_update")
   object Removed_Versions extends Function("removed_versions")
 
   object Invoke_Scala extends Function("invoke_scala")
   {
     def unapply(props: Properties.T): Option[(String, String, Boolean)] =
       props match {
         case List(PROPERTY, (NAME, name), (ID, id), ("thread", Value.Boolean(thread))) =>
           Some((name, id, thread))
         case _ => None
       }
   }
 
   object Cancel_Scala extends Function("cancel_scala")
   {
     def unapply(props: Properties.T): Option[String] =
       props match {
         case List(PROPERTY, (ID, id)) => Some(id)
         case _ => None
       }
   }
 
   val PRINT_OPERATIONS = "print_operations"
 
 
   /* export */
 
   val EXPORT = "export"
   val THEORY_NAME = "theory_name"
   val EXECUTABLE = "executable"
   val COMPRESS = "compress"
   val STRICT = "strict"
 
 
   /* debugger output */
 
   val DEBUGGER_STATE = "debugger_state"
   object Debugger_State
   {
     def unapply(props: Properties.T): Option[String] =
       props match {
         case List((FUNCTION, DEBUGGER_STATE), (NAME, name)) => Some(name)
         case _ => None
       }
   }
 
   val DEBUGGER_OUTPUT = "debugger_output"
   object Debugger_Output
   {
     def unapply(props: Properties.T): Option[String] =
       props match {
         case List((FUNCTION, DEBUGGER_OUTPUT), (NAME, name)) => Some(name)
         case _ => None
       }
   }
 
 
   /* simplifier trace */
 
   val SIMP_TRACE_PANEL = "simp_trace_panel"
 
   val SIMP_TRACE_LOG = "simp_trace_log"
   val SIMP_TRACE_STEP = "simp_trace_step"
   val SIMP_TRACE_RECURSE = "simp_trace_recurse"
   val SIMP_TRACE_HINT = "simp_trace_hint"
   val SIMP_TRACE_IGNORE = "simp_trace_ignore"
 
   val SIMP_TRACE_CANCEL = "simp_trace_cancel"
   object Simp_Trace_Cancel
   {
     def unapply(props: Properties.T): Option[Long] =
       props match {
         case (FUNCTION, SIMP_TRACE_CANCEL) :: Serial(i) => Some(i)
         case _ => None
       }
   }
 
 
   /* XML data representation */
 
   def encode: XML.Encode.T[Markup] = (markup: Markup) =>
   {
     import XML.Encode._
     pair(string, properties)((markup.name, markup.properties))
   }
 
   def decode: XML.Decode.T[Markup] = (body: XML.Body) =>
   {
     import XML.Decode._
     val (name, props) = pair(string, properties)(body)
     Markup(name, props)
   }
 }
 
 
 sealed case class Markup(name: String, properties: Properties.T)
 {
   def markup(s: String): String =
     YXML.string_of_tree(XML.Elem(this, List(XML.Text(s))))
 
   def update_properties(more_props: Properties.T): Markup =
     if (more_props.isEmpty) this
     else Markup(name, (more_props :\ properties) { case (p, ps) => Properties.put(ps, p) })
 
   def + (entry: Properties.Entry): Markup =
     Markup(name, Properties.put(properties, entry))
 }
diff --git a/src/Pure/Thy/thy_header.scala b/src/Pure/Thy/thy_header.scala
--- a/src/Pure/Thy/thy_header.scala
+++ b/src/Pure/Thy/thy_header.scala
@@ -1,268 +1,275 @@
 /*  Title:      Pure/Thy/thy_header.scala
     Author:     Makarius
 
 Static theory header information.
 */
 
 package isabelle
 
 
 import scala.util.parsing.input.Reader
 import scala.util.matching.Regex
 
 
 object Thy_Header
 {
   /* bootstrap keywords */
 
   type Keywords = List[(String, Keyword.Spec)]
   type Abbrevs = List[(String, String)]
 
   val CHAPTER = "chapter"
   val SECTION = "section"
   val SUBSECTION = "subsection"
   val SUBSUBSECTION = "subsubsection"
   val PARAGRAPH = "paragraph"
   val SUBPARAGRAPH = "subparagraph"
   val TEXT = "text"
   val TXT = "txt"
   val TEXT_RAW = "text_raw"
 
   val THEORY = "theory"
   val IMPORTS = "imports"
   val KEYWORDS = "keywords"
   val ABBREVS = "abbrevs"
   val AND = "and"
   val BEGIN = "begin"
 
   val bootstrap_header: Keywords =
     List(
       ("%", Keyword.Spec()),
       ("(", Keyword.Spec()),
       (")", Keyword.Spec()),
       (",", Keyword.Spec()),
       ("::", Keyword.Spec()),
       ("=", Keyword.Spec()),
       (AND, Keyword.Spec()),
       (BEGIN, Keyword.Spec(kind = Keyword.QUASI_COMMAND)),
       (IMPORTS, Keyword.Spec(kind = Keyword.QUASI_COMMAND)),
       (KEYWORDS, Keyword.Spec(kind = Keyword.QUASI_COMMAND)),
       (ABBREVS, Keyword.Spec(kind = Keyword.QUASI_COMMAND)),
       (CHAPTER, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (SECTION, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (SUBSECTION, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (SUBSUBSECTION, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (PARAGRAPH, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (SUBPARAGRAPH, Keyword.Spec(kind = Keyword.DOCUMENT_HEADING)),
       (TEXT, Keyword.Spec(kind = Keyword.DOCUMENT_BODY)),
       (TXT, Keyword.Spec(kind = Keyword.DOCUMENT_BODY)),
       (TEXT_RAW, Keyword.Spec(kind = Keyword.DOCUMENT_RAW)),
       (THEORY, Keyword.Spec(kind = Keyword.THY_BEGIN, tags = List("theory"))),
       ("ML", Keyword.Spec(kind = Keyword.THY_DECL, tags = List("ML"))))
 
   private val bootstrap_keywords =
     Keyword.Keywords.empty.add_keywords(bootstrap_header)
 
   val bootstrap_syntax: Outer_Syntax =
     Outer_Syntax.empty.add_keywords(bootstrap_header)
 
 
   /* file name vs. theory name */
 
   val PURE = "Pure"
   val ML_BOOTSTRAP = "ML_Bootstrap"
   val ml_roots = List("ROOT0.ML" -> "ML_Root0", "ROOT.ML" -> "ML_Root")
   val bootstrap_thys = List(PURE, ML_BOOTSTRAP).map(a => a -> ("Bootstrap_" + a))
 
   val bootstrap_global_theories =
     (Sessions.root_name :: (ml_roots ::: bootstrap_thys).map(_._2)).map(_ -> PURE)
 
   private val Thy_File_Name = new Regex(""".*?([^/\\:]+)\.thy""")
   private val Split_File_Name = new Regex("""(.*?)[/\\]*([^/\\:]+)""")
   private val File_Name = new Regex(""".*?([^/\\:]+)""")
 
   def is_base_name(s: String): Boolean =
     s != "" && !s.exists("/\\:".contains(_))
 
   def split_file_name(s: String): Option[(String, String)] =
     s match {
       case Split_File_Name(s1, s2) => Some((s1, s2))
       case _ => None
     }
 
   def import_name(s: String): String =
     s match {
       case File_Name(name) if !name.endsWith(".thy") => name
       case _ => error("Malformed theory import: " + quote(s))
     }
 
   def theory_name(s: String): String =
     s match {
       case Thy_File_Name(name) => bootstrap_name(name)
       case File_Name(name) =>
         if (name == Sessions.root_name) name
         else ml_roots.collectFirst({ case (a, b) if a == name => b }).getOrElse("")
       case _ => ""
     }
 
   def is_ml_root(theory: String): Boolean =
     ml_roots.exists({ case (_, b) => b == theory })
 
   def is_bootstrap(theory: String): Boolean =
     bootstrap_thys.exists({ case (_, b) => b == theory })
 
   def bootstrap_name(theory: String): String =
     bootstrap_thys.collectFirst({ case (a, b) if a == theory => b }).getOrElse(theory)
 
   def try_read_dir(dir: Path): List[String] =
   {
     val files =
       try { File.read_dir(dir) }
       catch { case ERROR(_) => Nil }
     for { Thy_File_Name(name) <- files } yield name
   }
 
 
   /* parser */
 
   trait Parser extends Parse.Parser
   {
     val header: Parser[Thy_Header] =
     {
       val load_command =
         ($$$("(") ~! (position(name) <~ $$$(")")) ^^ { case _ ~ x => x }) |
           success(("", Position.none))
 
       val keyword_kind = atom("outer syntax keyword specification", _.is_name)
       val keyword_spec =
         position(keyword_kind) ~ load_command ~ tags ^^
           { case (a, b) ~ c ~ d =>
               Keyword.Spec(kind = a, kind_pos = b,
                 load_command = c._1, load_command_pos = c._2, tags = d)
           }
 
       val keyword_decl =
         rep1(string) ~
         opt($$$("::") ~! keyword_spec ^^ { case _ ~ x => x }) ^^
         { case xs ~ y => xs.map((_, y.getOrElse(Keyword.Spec()))) }
 
       val keyword_decls =
         keyword_decl ~ rep($$$(AND) ~! keyword_decl ^^ { case _ ~ x => x }) ^^
         { case xs ~ yss => (xs :: yss).flatten }
 
       val abbrevs =
         rep1sep(rep1(text) ~ ($$$("=") ~! rep1(text)), $$$("and")) ^^
           { case res => for ((as ~ (_ ~ bs)) <- res; a <- as; b <- bs) yield (a, b) }
 
       val args =
         position(theory_name) ~
         (opt($$$(IMPORTS) ~! rep1(position(theory_name))) ^^
           { case None => Nil case Some(_ ~ xs) => xs }) ~
         (opt($$$(KEYWORDS) ~! keyword_decls) ^^
           { case None => Nil case Some(_ ~ xs) => xs }) ~
         (opt($$$(ABBREVS) ~! abbrevs) ^^
           { case None => Nil case Some(_ ~ xs) => xs }) ~
         $$$(BEGIN) ^^ { case a ~ b ~ c ~ d ~ _ => Thy_Header(a._1, a._2, b, c, d) }
 
       val heading =
         (command(CHAPTER) |
           command(SECTION) |
           command(SUBSECTION) |
           command(SUBSUBSECTION) |
           command(PARAGRAPH) |
           command(SUBPARAGRAPH) |
           command(TEXT) |
           command(TXT) |
           command(TEXT_RAW)) ~
         annotation ~! document_source
 
       (rep(heading) ~ command(THEORY) ~ annotation) ~! args ^^ { case _ ~ x => x }
     }
   }
 
 
   /* read -- lazy scanning */
 
   private def read_tokens(reader: Reader[Char], strict: Boolean): (List[Token], List[Token]) =
   {
     val token = Token.Parsers.token(bootstrap_keywords)
     def make_tokens(in: Reader[Char]): Stream[Token] =
       token(in) match {
         case Token.Parsers.Success(tok, rest) => tok #:: make_tokens(rest)
         case _ => Stream.empty
       }
 
     val all_tokens = make_tokens(reader)
     val drop_tokens =
       if (strict) Nil
       else all_tokens.takeWhile(tok => !tok.is_command(Thy_Header.THEORY)).toList
 
     val tokens = all_tokens.drop(drop_tokens.length)
     val tokens1 = tokens.takeWhile(tok => !tok.is_begin).toList
     val tokens2 = tokens.dropWhile(tok => !tok.is_begin).headOption.toList
 
     (drop_tokens, tokens1 ::: tokens2)
   }
 
   private object Parser extends Parser
   {
     def parse_header(tokens: List[Token], pos: Token.Pos): Thy_Header =
       parse(commit(header), Token.reader(tokens, pos)) match {
         case Success(result, _) => result
         case bad => error(bad.toString)
       }
   }
 
   def read(node_name: Document.Node.Name, reader: Reader[Char],
     command: Boolean = true,
     strict: Boolean = true): Thy_Header =
   {
     val (_, tokens0) = read_tokens(reader, true)
     val text = Scan.reader_decode_utf8(reader, Token.implode(tokens0))
 
     val (skip_tokens, tokens) = read_tokens(Scan.char_reader(text), strict)
     val pos =
       if (command) Token.Pos.command
       else (Token.Pos.file(node_name.node) /: skip_tokens)(_ advance _)
 
     Parser.parse_header(tokens, pos).map(Symbol.decode).check(node_name)
   }
 }
 
 sealed case class Thy_Header(
   name: String,
   pos: Position.T,
   imports: List[(String, Position.T)],
   keywords: Thy_Header.Keywords,
   abbrevs: Thy_Header.Abbrevs)
 {
   def map(f: String => String): Thy_Header =
     Thy_Header(f(name), pos,
       imports.map({ case (a, b) => (f(a), b) }),
       keywords.map({ case (a, spec) => (f(a), spec.map(f)) }),
       abbrevs.map({ case (a, b) => (f(a), f(b)) }))
 
   def check(node_name: Document.Node.Name): Thy_Header =
   {
     val base_name = node_name.theory_base_name
     if (Long_Name.is_qualified(name)) {
       error("Bad theory name " + quote(name) + " with qualification" + Position.here(pos))
     }
     if (base_name != name) {
       error("Bad theory name " + quote(name) + " for file " + Path.basic(base_name).thy +
         Position.here(pos) + Completion.report_theories(pos, List(base_name)))
     }
 
     for ((_, spec) <- keywords) {
       if (spec.kind != Keyword.THY_LOAD && spec.load_command.nonEmpty) {
         error("Illegal load command specification for kind: " + quote(spec.kind) +
           Position.here(spec.kind_pos))
       }
       if (!Command_Span.load_commands.exists(_.name == spec.load_command)) {
+        val completion =
+          for {
+            load_command <- Command_Span.load_commands
+            name = load_command.name
+            if name.startsWith(spec.load_command)
+          } yield (name, (Markup.LOAD_COMMAND, name))
         error("Unknown load command specification: " + quote(spec.load_command) +
-          Position.here(spec.load_command_pos))
+          Position.here(spec.load_command_pos) +
+          Completion.report_names(spec.load_command_pos, completion))
       }
     }
     this
   }
 }