diff --git a/src/Pure/Thy/document_build.scala b/src/Pure/Thy/document_build.scala
--- a/src/Pure/Thy/document_build.scala
+++ b/src/Pure/Thy/document_build.scala
@@ -1,581 +1,586 @@
 /*  Title:      Pure/Thy/document_build.scala
     Author:     Makarius
 
 Build theory document (PDF) from session database.
 */
 
 package isabelle
 
 
 object Document_Build {
   /* document variants */
 
   abstract class Document_Name {
     def name: String
     def path: Path = Path.basic(name)
 
     override def toString: String = name
   }
 
   object Document_Variant {
     def parse(opt: String): Document_Variant =
       Library.space_explode('=', opt) match {
         case List(name) => Document_Variant(name, Latex.Tags.empty)
         case List(name, tags) => Document_Variant(name, Latex.Tags(tags))
         case _ => error("Malformed document variant: " + quote(opt))
       }
   }
 
   sealed case class Document_Variant(name: String, tags: Latex.Tags) extends Document_Name {
     def print: String = if (tags.toString.isEmpty) name else name + "=" + tags.toString
   }
 
   sealed case class Document_Input(name: String, sources: SHA1.Digest)
   extends Document_Name { override def toString: String = name }
 
   sealed case class Document_Output(name: String, sources: SHA1.Digest, log_xz: Bytes, pdf: Bytes)
   extends Document_Name {
     override def toString: String = name
 
     def log: String = log_xz.uncompress().text
     def log_lines: List[String] = split_lines(log)
 
     def write(db: SQL.Database, session_name: String): Unit =
       write_document(db, session_name, this)
 
     def write(dir: Path): Path = {
       val path = dir + Path.basic(name).pdf
       Isabelle_System.make_directory(path.expand.dir)
       Bytes.write(path, pdf)
       path
     }
   }
 
 
   /* SQL data model */
 
   object Data {
     val session_name = SQL.Column.string("session_name").make_primary_key
     val name = SQL.Column.string("name").make_primary_key
     val sources = SQL.Column.string("sources")
     val log_xz = SQL.Column.bytes("log_xz")
     val pdf = SQL.Column.bytes("pdf")
 
     val table = SQL.Table("isabelle_documents", List(session_name, name, sources, log_xz, pdf))
 
     def where_equal(session_name: String, name: String = ""): SQL.Source =
       "WHERE " + Data.session_name.equal(session_name) +
         (if (name == "") "" else " AND " + Data.name.equal(name))
   }
 
   def read_documents(db: SQL.Database, session_name: String): List[Document_Input] = {
     val select = Data.table.select(List(Data.name, Data.sources), Data.where_equal(session_name))
     db.using_statement(select)(stmt =>
       stmt.execute_query().iterator({ res =>
         val name = res.string(Data.name)
         val sources = res.string(Data.sources)
         Document_Input(name, SHA1.fake_digest(sources))
       }).toList)
   }
 
   def read_document(
     db: SQL.Database,
     session_name: String,
     name: String
   ): Option[Document_Output] = {
     val select = Data.table.select(sql = Data.where_equal(session_name, name))
     db.using_statement(select)({ stmt =>
       val res = stmt.execute_query()
       if (res.next()) {
         val name = res.string(Data.name)
         val sources = res.string(Data.sources)
         val log_xz = res.bytes(Data.log_xz)
         val pdf = res.bytes(Data.pdf)
         Some(Document_Output(name, SHA1.fake_digest(sources), log_xz, pdf))
       }
       else None
     })
   }
 
   def write_document(db: SQL.Database, session_name: String, doc: Document_Output): Unit = {
     db.using_statement(Data.table.insert()){ stmt =>
       stmt.string(1) = session_name
       stmt.string(2) = doc.name
       stmt.string(3) = doc.sources.toString
       stmt.bytes(4) = doc.log_xz
       stmt.bytes(5) = doc.pdf
       stmt.execute()
     }
   }
 
 
   /* background context */
 
   def session_background(
     options: Options,
     session: String,
     dirs: List[Path] = Nil,
     progress: Progress = new Progress,
     verbose: Boolean = false
   ): Sessions.Background = {
       Sessions.load_structure(options + "document", dirs = dirs).
         selection_deps(Sessions.Selection.session(session), progress = progress, verbose = verbose).
         background(session)
   }
 
 
   /* document context */
 
   val texinputs: Path = Path.explode("~~/lib/texinputs")
 
   val isabelle_styles: List[Path] =
     List("isabelle.sty", "isabellesym.sty", "pdfsetup.sty", "railsetup.sty").
       map(name => texinputs + Path.basic(name))
 
   def running_script(title: String): String =
     "echo " + Bash.string("Running program \"" + title + "\" ...") + ";"
 
   def detect_running_script(s: String): Option[String] =
     for {
       s1 <- Library.try_unprefix("Running program \"", s)
       s2 <- Library.try_unsuffix("\" ...", s1)
     } yield s2
 
   sealed case class Document_Latex(
     name: Document.Node.Name,
     body: XML.Body,
     line_pos: Properties.T => Option[Int]
   ) {
     def content: File.Content_XML = File.content(Path.basic(tex_name(name)), body)
     def file_pos: String = File.symbolic_path(name.path)
     def write(latex_output: Latex.Output, dir: Path): Unit =
       content.output(latex_output.make(_, file_pos = file_pos, line_pos = line_pos))
         .write(dir)
   }
 
   def context(
     session_context: Export.Session_Context,
     document_session: Option[Sessions.Base] = None,
     document_selection: Document.Node.Name => Boolean = _ => true,
     progress: Progress = new Progress
   ): Context = new Context(session_context, document_session, document_selection, progress)
 
   final class Context private[Document_Build](
     val session_context: Export.Session_Context,
     document_session: Option[Sessions.Base],
     document_selection: Document.Node.Name => Boolean,
     val progress: Progress
   ) {
     context =>
 
 
     /* session info */
 
     private val base = document_session getOrElse session_context.session_base
     private val info = session_context.sessions_structure(base.session_name)
 
     def session: String = info.name
     def options: Options = info.options
 
     override def toString: String = session
 
     val classpath: List[File.Content] = session_context.classpath()
 
     def document_bibliography: Boolean = options.bool("document_bibliography")
 
     def document_logo: Option[String] =
       options.string("document_logo") match {
         case "" => None
         case "_" => Some("")
         case name => Some(name)
       }
 
     def document_build: String = options.string("document_build")
 
     def get_engine(): Engine = {
       val name = document_build
       Classpath(jar_contents = classpath).make_services(classOf[Engine])
         .find(_.name == name).getOrElse(error("Bad document_build engine " + quote(name)))
     }
 
 
     /* document content */
 
     def documents: List[Document_Variant] = info.documents
 
     def session_document_theories: List[Document.Node.Name] = base.proper_session_theories
     def all_document_theories: List[Document.Node.Name] = base.all_document_theories
 
     lazy val isabelle_logo: Option[File.Content] = {
       document_logo.map(logo_name =>
         Isabelle_System.with_tmp_file("logo", ext = "pdf") { tmp_path =>
           Logo.create_logo(logo_name, output_file = tmp_path, quiet = true)
           val path = Path.basic("isabelle_logo.pdf")
           val content = Bytes.read(tmp_path)
           File.content(path, content)
         })
     }
 
     lazy val session_graph: File.Content = {
       val path = Browser_Info.session_graph_path
       val content = graphview.Graph_File.make_pdf(options, base.session_graph_display)
       File.content(path, content)
     }
 
     lazy val session_tex: File.Content = {
       val path = Path.basic("session.tex")
       val content =
         Library.terminate_lines(
           session_document_theories.map(name => "\\input{" + tex_name(name) + "}"))
       File.content(path, content)
     }
 
     lazy val document_latex: List[Document_Latex] =
       for (name <- all_document_theories)
       yield {
+        val selected = document_selection(name)
+
         val body =
-          if (document_selection(name)) {
+          if (selected) {
             val entry = session_context(name.theory, Export.DOCUMENT_LATEX, permissive = true)
             YXML.parse_body(entry.text)
           }
           else Nil
 
         def line_pos(props: Properties.T): Option[Int] =
           Position.Line.unapply(props) orElse {
-            for {
-              snapshot <- session_context.document_snapshot
-              id <- Position.Id.unapply(props)
-              offset <- Position.Offset.unapply(props)
-              line <- snapshot.find_command_line(id, offset)
-            } yield line
+            if (selected) {
+              for {
+                snapshot <- session_context.document_snapshot
+                id <- Position.Id.unapply(props)
+                offset <- Position.Offset.unapply(props)
+                line <- snapshot.find_command_line(id, offset)
+              } yield line
+            }
+            else None
           }
 
         Document_Latex(name, body, line_pos)
       }
 
 
     /* build document */
 
     def build_document(doc: Document_Variant, verbose: Boolean = false): Document_Output = {
       Isabelle_System.with_tmp_dir("document") { tmp_dir =>
         val engine = get_engine()
         val directory = engine.prepare_directory(context, tmp_dir, doc)
         engine.build_document(context, directory, verbose)
       }
     }
 
 
     /* document directory */
 
     def make_directory(dir: Path, doc: Document_Variant): Path =
       Isabelle_System.make_directory(dir + Path.basic(doc.name))
 
     def prepare_directory(
       dir: Path,
       doc: Document_Variant,
       latex_output: Latex.Output
     ): Directory = {
       val doc_dir = make_directory(dir, doc)
 
 
       /* actual sources: with SHA1 digest */
 
       isabelle_styles.foreach(Latex.copy_file(_, doc_dir))
 
       val comment_latex = latex_output.options.bool("document_comment_latex")
       if (!comment_latex) Latex.copy_file(texinputs + Path.basic("comment.sty"), doc_dir)
       doc.tags.sty(comment_latex).write(doc_dir)
 
       for ((base_dir, src) <- info.document_files) {
         Latex.copy_file_base(info.dir + base_dir, src, doc_dir)
       }
 
       session_tex.write(doc_dir)
       document_latex.foreach(_.write(latex_output, doc_dir))
 
       val root_name1 = "root_" + doc.name
       val root_name = if ((doc_dir + Path.explode(root_name1).tex).is_file) root_name1 else "root"
 
       val digests1 = List(doc.print, document_logo.toString, document_build).map(SHA1.digest)
       val digests2 = File.find_files(doc_dir.file, follow_links = true).map(SHA1.digest)
       val sources = SHA1.digest_set(digests1 ::: digests2)
 
 
       /* derived material: without SHA1 digest */
 
       isabelle_logo.foreach(_.write(doc_dir))
       session_graph.write(doc_dir)
 
       Directory(doc_dir, doc, root_name, sources)
     }
 
     def old_document(directory: Directory): Option[Document_Output] =
       for {
         db <- session_context.session_db()
         old_doc <- read_document(db, session, directory.doc.name)
         if old_doc.sources == directory.sources
       }
       yield old_doc
   }
 
   sealed case class Directory(
     doc_dir: Path,
     doc: Document_Variant,
     root_name: String,
     sources: SHA1.Digest
   ) {
     def root_name_script(ext: String = ""): String =
       Bash.string(if (ext.isEmpty) root_name else root_name + "." + ext)
 
     def conditional_script(
       ext: String, exe: String, title: String = "", after: String = ""
     ): String = {
       "if [ -f " + root_name_script(ext) + " ]\n" +
       "then\n" +
       "  " + (if (title.nonEmpty) running_script(title) else "") +
         exe + " " + root_name_script() + "\n" +
       (if (after.isEmpty) "" else "  " + after) +
       "fi\n"
     }
 
     def log_errors(): List[String] =
       Latex.latex_errors(doc_dir, root_name) :::
       Bibtex.bibtex_errors(doc_dir, root_name)
 
     def make_document(log: List[String], errors: List[String]): Document_Output = {
       val root_pdf = Path.basic(root_name).pdf
       val result_pdf = doc_dir + root_pdf
 
       if (errors.nonEmpty) {
         val message = "Failed to build document " + quote(doc.name)
         throw new Build_Error(log, errors ::: List(message))
       }
       else if (!result_pdf.is_file) {
         val message = "Bad document result: expected to find " + root_pdf
         throw new Build_Error(log, List(message))
       }
       else {
         val log_xz = Bytes(cat_lines(log)).compress()
         val pdf = Bytes.read(result_pdf)
         Document_Output(doc.name, sources, log_xz, pdf)
       }
     }
   }
 
 
   /* build engines */
 
   abstract class Engine(val name: String) extends Isabelle_System.Service {
     override def toString: String = name
 
     def prepare_directory(context: Context, dir: Path, doc: Document_Variant): Directory
     def build_document(context: Context, directory: Directory, verbose: Boolean): Document_Output
   }
 
   abstract class Bash_Engine(name: String) extends Engine(name) {
     def prepare_directory(context: Context, dir: Path, doc: Document_Variant): Directory =
       context.prepare_directory(dir, doc, new Latex.Output(context.options))
 
     def use_pdflatex: Boolean = false
     def running_latex: String = running_script(if (use_pdflatex) "pdflatex" else "lualatex")
     def latex_script(context: Context, directory: Directory): String =
       running_latex + (if (use_pdflatex) "$ISABELLE_PDFLATEX" else "$ISABELLE_LUALATEX") +
         " " + directory.root_name_script() + "\n"
 
     def bibtex_script(context: Context, directory: Directory, latex: Boolean = false): String = {
       val ext = if (context.document_bibliography) "aux" else "bib"
       directory.conditional_script(ext, "$ISABELLE_BIBTEX", title = "bibtex",
         after = if (latex) latex_script(context, directory) else "")
     }
 
     def makeindex_script(context: Context, directory: Directory, latex: Boolean = false): String =
       directory.conditional_script("idx", "$ISABELLE_MAKEINDEX", title = "makeindex",
         after = if (latex) latex_script(context, directory) else "")
 
     def use_build_script: Boolean = false
     def build_script(context: Context, directory: Directory): String = {
       val has_build_script = (directory.doc_dir + Path.explode("build")).is_file
 
       if (!use_build_script && has_build_script) {
         error("Unexpected document build script for option document_build=" +
           quote(context.document_build))
       }
       else if (use_build_script && !has_build_script) error("Missing document build script")
       else if (has_build_script) "./build pdf " + Bash.string(directory.doc.name)
       else {
         "set -e\n" +
         latex_script(context, directory) +
         bibtex_script(context, directory, latex = true) +
         makeindex_script(context, directory) +
         latex_script(context, directory) +
         makeindex_script(context, directory, latex = true)
       }
     }
 
     def build_document(
       context: Context,
       directory: Directory,
       verbose: Boolean
     ): Document_Output = {
       val result =
         context.progress.bash(
           build_script(context, directory),
           cwd = directory.doc_dir.file,
           echo = verbose,
           watchdog = Time.seconds(0.5))
 
       val log = result.out_lines ::: result.err_lines
       val err = result.err
 
       val errors1 = directory.log_errors()
       val errors2 =
         if (result.ok) errors1
         else if (err.nonEmpty) err :: errors1
         else if (errors1.nonEmpty) errors1
         else List("Error")
       directory.make_document(log, errors2)
     }
   }
 
   class LuaLaTeX_Engine extends Bash_Engine("lualatex")
   class PDFLaTeX_Engine extends Bash_Engine("pdflatex") { override def use_pdflatex: Boolean = true }
   class Build_Engine extends Bash_Engine("build") { override def use_build_script: Boolean = true }
 
   class LIPIcs_Engine(name: String) extends Bash_Engine(name) {
     def lipics_options(options: Options): Options =
       options + "document_heading_prefix=" + "document_comment_latex"
 
     override def use_pdflatex: Boolean = true
 
     override def prepare_directory(context: Context, dir: Path, doc: Document_Variant): Directory = {
       val doc_dir = context.make_directory(dir, doc)
       Build_LIPIcs.document_files.foreach(Latex.copy_file(_, doc_dir))
 
       val latex_output = new Latex.Output(lipics_options(context.options))
       context.prepare_directory(dir, doc, latex_output)
     }
   }
   class LIPIcs_LuaLaTeX_Engine extends LIPIcs_Engine("lipics")
   class LIPIcs_PDFLaTeX_Engine extends LIPIcs_Engine("lipics_pdflatex") {
     override def use_pdflatex: Boolean = true
   }
 
 
   /* build documents */
 
   def tex_name(name: Document.Node.Name): String = name.theory_base_name + ".tex"
 
   class Build_Error(val log_lines: List[String], val log_errors: List[String])
     extends Exn.User_Error(Exn.cat_message(log_errors: _*))
 
   def build_documents(
     context: Context,
     output_sources: Option[Path] = None,
     output_pdf: Option[Path] = None,
     verbose: Boolean = false
   ): List[Document_Output] = {
     val progress = context.progress
     val engine = context.get_engine()
 
     val documents =
       for (doc <- context.documents)
       yield {
         Isabelle_System.with_tmp_dir("document") { tmp_dir =>
           progress.echo("Preparing " + context.session + "/" + doc.name + " ...")
           val start = Time.now()
 
           output_sources.foreach(engine.prepare_directory(context, _, doc))
           val directory = engine.prepare_directory(context, tmp_dir, doc)
 
           val document =
             context.old_document(directory) getOrElse
               engine.build_document(context, directory, verbose)
 
           val stop = Time.now()
           val timing = stop - start
 
           progress.echo("Finished " + context.session + "/" + doc.name +
             " (" + timing.message_hms + " elapsed time)")
 
           document
         }
       }
 
     for (dir <- output_pdf; doc <- documents) {
       val path = doc.write(dir)
       progress.echo("Document at " + path.absolute)
     }
 
     documents
   }
 
 
   /* Isabelle tool wrapper */
 
   val isabelle_tool =
     Isabelle_Tool("document", "prepare session theory document", Scala_Project.here,
       { args =>
         var output_sources: Option[Path] = None
         var output_pdf: Option[Path] = None
         var verbose_latex = false
         var dirs: List[Path] = Nil
         var options = Options.init()
         var verbose_build = false
 
         val getopts = Getopts("""
 Usage: isabelle document [OPTIONS] SESSION
 
   Options are:
     -O DIR       output directory for LaTeX sources and resulting PDF
     -P DIR       output directory for resulting PDF
     -S DIR       output directory for LaTeX sources
     -V           verbose latex
     -d DIR       include session directory
     -o OPTION    override Isabelle system OPTION (via NAME=VAL or NAME)
     -v           verbose build
 
   Prepare the theory document of a session.
 """,
           "O:" -> (arg =>
             {
               val dir = Path.explode(arg)
               output_sources = Some(dir)
               output_pdf = Some(dir)
             }),
           "P:" -> (arg => { output_pdf = Some(Path.explode(arg)) }),
           "S:" -> (arg => { output_sources = Some(Path.explode(arg)) }),
           "V" -> (_ => verbose_latex = true),
           "d:" -> (arg => dirs = dirs ::: List(Path.explode(arg))),
           "o:" -> (arg => options = options + arg),
           "v" -> (_ => verbose_build = true))
 
         val more_args = getopts(args)
         val session =
           more_args match {
             case List(a) => a
             case _ => getopts.usage()
           }
 
         val progress = new Console_Progress(verbose = verbose_build)
 
         progress.interrupt_handler {
           val build_results =
             Build.build(options, selection = Sessions.Selection.session(session),
               dirs = dirs, progress = progress, verbose = verbose_build)
           if (!build_results.ok) error("Failed to build session " + quote(session))
 
           if (output_sources.isEmpty && output_pdf.isEmpty) {
             progress.echo_warning("No output directory")
           }
 
           val session_background = Document_Build.session_background(options, session, dirs = dirs)
           using(Export.open_session_context(build_results.store, session_background)) {
             session_context =>
               build_documents(
                 context(session_context, progress = progress),
                 output_sources = output_sources, output_pdf = output_pdf,
                 verbose = verbose_latex)
           }
         }
       })
 }