diff --git a/doc/texinfo/opt_plugin.texi b/doc/texinfo/opt_plugin.texi
index 1c55f73ba17ebffe90db8bbf11790e65f6b86d47..a1e8ad7a6c6279d9a143dad35b36596553a322f2 100644
--- a/doc/texinfo/opt_plugin.texi
+++ b/doc/texinfo/opt_plugin.texi
@@ -161,7 +161,7 @@ Plugin(Evaluate) is executed in-place.
 String options:
 @table @code
 @item Expression
-Default value: @code{"v * (x+y+z)"}
+Default value: @code{"Sin(v) * Sqrt(x^2+y^2)"}
 @end table
 Numeric options:
 @table @code