clarified options: support lualatex as well, but prefer old pdflatex for demos;

--- a/etc/build.props	Sat Nov 05 14:29:19 2022 +0100
+++ b/etc/build.props	Sat Nov 05 14:41:51 2022 +0100
@@ -297,7 +297,8 @@
   isabelle.Bash$Handler \
   isabelle.Bibtex$File_Format \
   isabelle.Document_Build$Build_Engine \
-  isabelle.Document_Build$LIPIcs_Engine \
+  isabelle.Document_Build$LIPIcs_LuaLaTeX_Engine \
+  isabelle.Document_Build$LIPIcs_PDFLaTeX_Engine \
   isabelle.Document_Build$LuaLaTeX_Engine \
   isabelle.Document_Build$PDFLaTeX_Engine \
   isabelle.CI_Builds \

--- a/src/Doc/Demo_LIPIcs/ROOT	Sat Nov 05 14:29:19 2022 +0100
+++ b/src/Doc/Demo_LIPIcs/ROOT	Sat Nov 05 14:41:51 2022 +0100
@@ -1,8 +1,10 @@
-chapter Doc
+chapter Doc  (*Isabelle documentation*)
 
 session Demo_LIPIcs (doc) = HOL +
-  options [document_variants = "demo_lipics",
-    document_build = "lipics"]
+  options [
+    document_variants = "demo_lipics",  (*Isabelle documentation*)
+    document_build = "lipics_pdflatex"  (*or: "lipics" for LuaLaTeX*)
+  ]
   theories
     Document
   document_files

--- a/src/Doc/Demo_LLNCS/ROOT	Sat Nov 05 14:29:19 2022 +0100
+++ b/src/Doc/Demo_LLNCS/ROOT	Sat Nov 05 14:41:51 2022 +0100
@@ -1,7 +1,10 @@
-chapter Doc
+chapter Doc  (*Isabelle documentation*)
 
 session Demo_LLNCS (doc) = HOL +
-  options [document_variants = "demo_llncs"]
+  options [
+    document_variants = "demo_llncs",  (*Isabelle documentation*)
+    document_build = "pdflatex"  (*or: omit option for LuaLaTeX*)
+  ]
   theories
     Document
   document_files (in "$ISABELLE_LLNCS_HOME")

--- a/src/Pure/Thy/document_build.scala	Sat Nov 05 14:29:19 2022 +0100
+++ b/src/Pure/Thy/document_build.scala	Sat Nov 05 14:41:51 2022 +0100
@@ -386,7 +386,7 @@
   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 extends Bash_Engine("lipics") {
+  class LIPIcs_Engine(name: String) extends Bash_Engine(name) {
     def lipics_options(options: Options): Options =
       options + "document_heading_prefix=" + "document_comment_latex"
 
@@ -400,6 +400,10 @@
       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 */