fix the complexity comments for attribute APIs

sky/specs/parsing.md

 Parsing
 =======
 
 Parsing in Sky is a strict pipeline consisting of five stages:
 
 - decoding, which converts incoming bytes into Unicode characters
   using UTF-8.
 
 - normalising, which manipulates the sequence of characters.
 
@@ skipping 751 matching lines @@
 -------------------
 
 Replace each sequence of character tokens with a single string token
 whose value is the concatenation of all the characters in the
 character tokens.
 
 For each start tag token, remove all but the first name/value pair for
 each name (i.e. remove duplicate attributes, keeping only the first
 one).
 
+TODO(ianh): maybe sort the attributes?
+
 For each end tag token, remove the attributes entirely.
 
 If the token is a start tag token, notify the JavaScript token stream
 callback of the token.
 
 Then, pass the tokens to the tree construction stage.
 
 
 Tree construction stage
 -----------------------
@@ skipping 27 matching lines @@
         there isn't one, skip this token.
      2. If there's a ``template`` element in the _stack of open
         nodes_ above _node_, then skip this token.
      3. Pop nodes from the _stack of open nodes_ until _node_ has been
         popped.
      4. If _node_'s tag name is ``script``, then yield until there
         are no pending import loads, then execute the script given by
         the element's contents.
 3. Yield until there are no pending import loads.
 3. Fire a ``load`` event at the _parsing context_ object.