src/Pure/Admin/build_doc.scala

     progress.echo("Build started for documentation " + commas_quote(documents))
     val doc_options =
       options + "document=pdf" + "document_output=~~/doc" + "document_output_sources=false"
     val deps = Sessions.load_structure(doc_options).selection_deps(selection)
     for (session <- selection.sessions) {
+      progress.expose_interrupt()
       Present.build_documents(session, deps, store, progress = progress)
     }
   }