list-filter-expr is a bracket-specifier. (#76)

* `list-filter-expr` is a `bracket-specifier`.

* Maintain correct order for list-filter-expr documentation

Co-authored-by: Nolan Woods <[email protected]>

Author: springcomp

GRAMMAR.ABNF

@@ -47,7 +47,7 @@
 ;;
 ;; %%GRAMMAR%%
 
-expression        = sub-expression / index-expression  / comparator-expression / list-filter-expr
+expression        = sub-expression / index-expression  / comparator-expression
 expression        =/ or-expression / identifier
 expression        =/ and-expression / not-expression / paren-expression
 expression        =/ multi-select-list / multi-select-hash / literal
@@ -380,6 +380,7 @@ bracket-specifier =/ "[" "*" "]"
 ;; ```
 
 list-filter-expr = "[?" expression "]" ;; # Filter Expressions \
+bracket-specifier =/ list-filter-expr ;; \
 comparator-expression = expression comparator expression ;; \
 comparator        = "<" / "<=" / "==" / ">=" / ">" / "!="
 ;; A filter expression provides a way to select JSON elements based on a comparison to another expression. A filter