--- a/RelaxNG/publiquiz.rnc	mar. oct. 23 18:39:42 2018 +0200
+++ b/RelaxNG/publiquiz.rnc	mer. nov. 07 16:51:10 2018 +0100
@@ -1212,7 +1212,7 @@
 mistake = element mistake { mistake.attributes, mistake.content }
 
 mistake.attributes =
-   mistake.is.attribute
+   mistake.is.attribute?
 mistake.is.attribute = attribute is { text }
 
 mistake.content = inlines