clarify sort_natural and fix unless syntax

document forloop.parentloop

lib/liquid/forloop_drop.rb

@@ -15,12 +15,19 @@ module Liquid
     end
 
     # @liquid_public_docs
-    # @liquid_name forloop.length
+    # @liquid_name length
     # @liquid_summary
     #   The total number of iterations in the loop.
     # @liquid_return [number]
     attr_reader :length
 
+    # @liquid_public_docs
+    # @liquid_name parentloop
+    # @liquid_summary
+    #   The parent `forloop` object.
+    # @liquid_description
+    #   If the current `for` loop isn't nested inside another `for` loop, then `nil` is returned.
+    # @liquid_return [forloop]
     attr_reader :parentloop
 
     def name

lib/liquid/standardfilters.rb

@@ -358,7 +358,11 @@ module Liquid
     # @liquid_type filter
     # @liquid_category array
     # @liquid_summary
-    #   Sorts the items in an array in case-insensitive alphabetical, or numerical, order.
+    #   Sorts the items in an array in case-insensitive alphabetical order.
+    # @liquid_description
+    #   > Caution:
+    #   > You shouldn't use the `sort_natural` filter to sort numerical values. When comparing items an array, each item is converted to a
+    #   > string, so sorting on numerical values can lead to unexpected results.
     # @liquid_syntax array | sort_natural
     # @liquid_return [array[untyped]]
     def sort_natural(input, property = nil)

lib/liquid/tags/unless.rb

@@ -15,7 +15,7 @@ module Liquid
   # @liquid_syntax
   #   {% unless condition %}
   #     expression
-  #   {% endif %}
+  #   {% endunless %}
   # @liquid_syntax_keyword condition The condition to evaluate.
   # @liquid_syntax_keyword expression The expression to render unless the condition is met.
   class Unless < If

lib/liquid/variable_lookup.rb

@@ -32,6 +32,10 @@ module Liquid
       end
     end
 
+    def lookup_command?(lookup_index)
+      @command_flags & (1 << lookup_index) != 0
+    end
+
     def evaluate(context)
       name   = context.evaluate(@name)
       object = context.find_variable(name)
@@ -55,7 +59,7 @@ module Liquid
           # Some special cases. If the part wasn't in square brackets and
           # no key with the same name was found we interpret following calls
           # as commands and call them on the current object
-        elsif @command_flags & (1 << i) != 0 && object.respond_to?(key)
+        elsif lookup_command?(i) && object.respond_to?(key)
           object = object.send(key).to_liquid
 
           # No key was present with the desired value and it wasn't one of the directly supported