src/Doc/ROOT

--- a/src/Doc/ROOT	Mon May 25 22:37:14 2020 +0200
+++ b/src/Doc/ROOT	Mon May 25 22:37:22 2020 +0200
@@ -378,7 +378,7 @@
     "root.tex"
 
 session System (doc) in "System" = Pure +
-  options [document_variants = "system", thy_output_source]
+  options [document_variants = "system", thy_output_source, pide_session]
   sessions
     "HOL-Library"
   theories