Counter set always allows alphabetic values regardless of org-list-allow-alphabetical.

src/parser/plain_list.rs

@@ -166,12 +166,8 @@ fn plain_list_item<'b, 'g, 'r, 's>(
         |(_bullet_type, bull)| Into::<&str>::into(bull) != "*" || indent_level > 0,
     )(remaining)?;
 
-    let (remaining, _maybe_counter_set) = opt(tuple((
+    let (remaining, _maybe_counter_set) =
-        space1,
+        opt(tuple((space1, tag("[@"), counter_set_value, tag("]"))))(remaining)?;
-        tag("[@"),
-        parser_with_context!(counter)(context),
-        tag("]"),
-    )))(remaining)?;
 
     let (remaining, maybe_checkbox) = opt(tuple((space1, item_checkbox)))(remaining)?;
 
@@ -314,6 +310,16 @@ fn counter<'b, 'g, 'r, 's>(
     }
 }
 
+#[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
+fn counter_set_value<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    alt((
+        recognize(one_of(
+            "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ",
+        )),
+        digit1,
+    ))(input)
+}
+
 #[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
 fn plain_list_end<'b, 'g, 'r, 's>(
     _context: RefContext<'b, 'g, 'r, 's>,