add a tagging system to the website

content/programming/lua/classes.tree

@@ -301,7 +301,7 @@ local Player = Entity:inherit()
     ```lua
     local Cat = {}
     -- We still need to override __index, so that the metatable we set in our own constructor
-    -- has our overridden `speak()` method. 
+    -- has our overridden `speak()` method.
     Cat.__index = Cat
     -- To be able to call `Animal` methods from `Cat`, we set it as its metatable.
     -- Remember that `Animal.__index == Animal`.
@@ -380,7 +380,7 @@ local Player = Entity:inherit()
     -- insert below the `end` of `function Class:inherit()`
 
     -- By default, let's make the base `Class` impossible to instantiate.
-    -- This should catch bugs if a subclass forgets to override `initialize`. 
+    -- This should catch bugs if a subclass forgets to override `initialize`.
     function Class:initialize()
         error("this class cannot be initialized")
     end
@@ -462,7 +462,7 @@ local Player = Entity:inherit()
 
         % id = "01JKKQHG5DQW7G1HDWYGX4WEYC"
         - our class library implements a Ruby-style `Object:new(args)` function for constructing new instances of our class.
-        Python however, uses the syntax `Object(args)` for constructing instances of objects. 
+        Python however, uses the syntax `Object(args)` for constructing instances of objects.
         can you think of a way to make our class library use the Python-style syntax?
 
         % id = "01JKKQHG5D7QN029A3F1B6SYC2"