Do not allow elements to immediately nest inside themselves.

Plain list is omitted because they can nest.

src/parser/plain_list.rs

@@ -35,8 +35,9 @@ use tracing::span;
 
 #[tracing::instrument(ret, level = "debug")]
 pub fn plain_list<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, PlainList<'s>> {
-    let parser_context =
-        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+    let parser_context = context
+        .with_additional_node(ContextElement::Context("plain list"))
+        .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
             class: ExitClass::Beta,
             exit_matcher: &plain_list_end,
         }));