Specs: clean up the last remaining mentions of documents

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 765 matching lines @@
 
 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
 -----------------------
 
-To construct a node tree from a _sequence of tokens_ and a document
-_document_ (this is implemented in JS):
+To construct a node tree from a _sequence of tokens_ and an element
+tree rooted at a `Root` node _root_ (this is implemented in JS):
 
-1. Initialize the _stack of open nodes_ to be _document_.
+1. Initialize the _stack of open nodes_ to be _root_.
 2. Initialize _imported modules_ to an empty list.
 3. Consider each token _token_ in the _sequence of tokens_ in turn, as
    follows. If a token is to be skipped, then jump straight to the
    next token, without doing any more work with the skipped token.
    - If _token_ is a string token,
      1. If the value of the token contains only U+0020 and U+000A
         characters, and there is no ``t`` element on the _stack of
         open nodes_, then skip the token.
      2. Create a text node _node_ whose character data is the value of
         the token.
      3. Append _node_ to the top node in the _stack of open nodes_.
    - If _token_ is a start tag token,
      1. If the tag name isn't a registered tag name, then yield until
         _imported modules_ contains no entries with unresolved
         promises.
      2. If the tag name is not registered, then let the ErrorElement
         constructor from dart:sky be the element constructor.
         Otherwise, let the element constructor be the registered
         element's constructor for that tag name in this module.
      3. Create an element _node_ with the attributes given by the
         token by calling the constructor.
      4. If _node_ is not an Element object, then let the constructor
         be the ErrorElement constructor and return to the previous
         step.
      5. Append _node_ to the top node in the _stack of open nodes_.
      6. Push _node_ onto the top of the _stack of open nodes_.
      7. If _node_ is a ``template`` element, then:
-        1. Let _fragment_ be the ``DocumentFragment`` object that the
-           ``template`` element uses as its template contents container.
+        1. Let _fragment_ be the ``Fragment`` object that the
+           ``template`` element uses as its template contents
+           container.
         2. Push _fragment_ onto the top of the _stack of open nodes_.
         If _node_ is an ``import`` element, then:
         1. Let ``url`` be the value of _node_'s ``src`` attribute.
         2. Call ``parsing context``'s ``importModule()`` method,
            passing it ``url``.
         3. Add the returned promise to _imported modules_; if _node_
            has an ``as`` attribute, associate the entry with that
            name.
    - If _token_ is an end tag token:
      1. If the tag name is registered, let _tag name_ be that tag
         name. Otherwise, let _tag name_ be "error".
      2. Let _node_ be the topmost node in the _stack of open nodes_
         whose tag name is _tag name_, if any. If there isn't one, skip
         this token.
      3. If there's a ``template`` element in the _stack of open
         nodes_ above _node_, then skip this token.
      4. Pop nodes from the _stack of open nodes_ until _node_ has been
         popped.
      5. If _node_'s tag name is ``script``, then yield until _imported
         modules_ contains no entries with unresolved promises, then
         execute the script given by the element's contents, using the
         associated names as appropriate.
    - If _token_ is an automatic end tag token:
      1. Pop the top node from the _stack of open nodes_, unless it is
-        the document.
+        the _root_ node.
 4. Yield until _imported modules_ has no promises.
 5. Fire a ``load`` event at the _parsing context_ object.