src/Pure/System/isabelle_fonts.scala

--- a/src/Pure/System/isabelle_fonts.scala	Wed Nov 28 11:41:49 2018 +0100
+++ b/src/Pure/System/isabelle_fonts.scala	Wed Nov 28 11:43:06 2018 +0100
@@ -10,6 +10,13 @@
 
 object Isabelle_Fonts
 {
+  /* standard names */
+
+  val mono: String = "Isabelle DejaVu Sans Mono"
+  val sans: String = "Isabelle DejaVu Sans"
+  val serif: String = "Isabelle DejaVu Serif"
+
+
   /* Isabelle system environment */
 
   def variables(html: Boolean = false): List[String] =