[Specs] Remove all the obsolete specs.

sky/specs/markup.md

-Sky Markup: Syntax
-==================
-
-A Sky file must consist of the following components:
-
- 1. If the file is intended to be a top-level Sky application, the
-    string "``#!mojo mojo:sky``" followed by a U+0020, U+000A or
-    U+000D character.
-
-    If the file is intended to be a module, then the string "SKY", a
-    U+0020 (space) character, the string "MODULE", and a U+0020,
-    U+000A or U+000D character.
-
-    These signatures make it more difficult to e.g. embed some Sky
-    markup into a PNG and then cause someone to import that image as a
-    module.
-
- 2. Zero or more of the following, in any order:
-     - comments
-     - text
-     - escapes
-     - elements
-
-Sky files must be encoded using UTF-8.
-
-A file that doesn't begin with the "``#!mojo mojo:sky``" signature
-isn't a Sky application file. For example:
-
-    #!mojo https://example.com/runtimes/sky.asmjs
-    Hello World
-
-...is not a Sky file, even if ``https://example.com/runtimes/sky.asmjs``
-is an implementation of the Sky runtime: it's just a file intended
-specifically for that runtime.
-
-The ``mojo:sky`` URL represents the generic Sky runtime provided by
-your Mojo runtime vendor.
-
-
-Comments
---------
-
-Comments start with the sequence "``<!--``" and end with the
-sequence "``-->``", where the start and end hyphens don't overlap.
-In between these characters, any sequence of characters is allowed
-except "``-->``", which terminates the comment. Comments cannot,
-therefore, be nested.
-
-
-Text
-----
-
-Any sequence of Unicode characters other than ``<``, ``&``, and
-U+0000.
-
-
-Escapes
--------
-
-There are three kinds of escapes:
-
-### Hex
-
-They begin with the sequence ``&#x`` or ``&#X``, followed by a
-sequence of hex characters (lowercase or uppercase), followed by a
-semicolon. The number 0 is not allowed.
-
-### Decimal
-
-They begin with the sequence ``&#`` or ``&#``, followed by a
-sequence of decimal characters, followed by a semicolon. The number 0
-is not allowed.
-
-### Named
-
-They begin with the sequence ``&``, followed by any characters,
-followed by a semicolon.
-
-The following names work:
-
-| Name | Character | Unicode |
-| ---- | --------- | ------- |
-| `lt` | `<` | U+003C LESS-THAN SIGN character |
-| `gt` | `>` | U+003E GREATER-THAN SIGN character |
-| `amp` | `&` | U+0026 AMPERSAND character |
-| `apos` | `'` | U+0027 APOSTROPHE character |
-| `quot` | `"` | U+0022 QUOTATION MARK character |
-
-
-Elements
---------
-
-An element consists of the following:
-
-1. ``<``
-2. Tag name: A sequence of characters other than ``/``, ``>``,
-   U+0020, U+000A, U+000D (whitespace).
-3. Zero or more of the following:
-   1. One or more U+0020, U+000A, U+000D (whitespace).
-   2. Attribute name: A sequence of characters other than ``/``,
-      ``=``, ``>``, U+0020, U+000A, U+000D (whitespace).
-   3. Optionally:
-      1. Zero or more U+0020, U+000A, U+000D (whitespace) characters.
-      2. ``=``
-      3. Zero or more U+0020, U+000A, U+000D (whitespace) characters.
-      4. Attribute value: Either:
-         - ``'`` followed by attribute text other than ``'``
-           followed by a terminating ``'``.
-         - ``"`` followed by attribute text other than ``'``
-           followed by a terminating ``"``.
-         - attribute text other than ``/``, ``>``,
-           U+0020, U+000A, U+000D (whitespace).
-         "Attribute text" is escapes or any unicode characters other
-         than U+0000.
-4. Either:
-   - For a void element:
-     1. ``/``, indicating an empty element.
-     2. ``>``
-   - For a non-void element:
-     2. ``>``
-     3. The element's contents:
-        - If the element's tag name is ``script``, then any sequence of
-          characters other than U+0000, but there must not be the
-          substring ``</script``. The sequence must be valid sky script.
-        - If the element's tag name is ``style``, then any sequence of
-          characters other than U+0000, but there must not be the
-          substring ``</style``. The sequence must be valid sky style.
-        - Otherwise, zero or more of the following, in any order:
-          - comments
-          - text
-          - escapes
-          - elements
-     4. Finally, the end tag, which may be omitted if the element's tag
-        name is not ``template``, consisting of:
-        1. ``<``
-        2. ``/``
-        3. Same sequence of characters as "tag name" above; this may
-           be omitted if no start tags have had their end tag omitted
-           since this element's start tag, unless this element's tag
-           name is ``script`` or ``style``.
-        4. ``>``
-
-
-Sky Markup: Elements
-====================
-
-The Sky language consists of very few elements, since it is expected
-that everything of note would be provided by frameworks.
-
-The following elements are implicitly registered by default, even if
-you haven't imported anything. You can get to their constructors if
-you import dart:sky (basically, dart:sky is always imported by defaul;
-it's the runtime library). None of these elements have shadow trees.
-
-``<import src="foo.sky">``
- - Downloads and imports foo.sky in the background.
-
-``<import src="foo.sky" as="foo">``
- - Downloads and imports foo.sky in the background, using "foo" as its
-   local name (see ``<script>``).
-
-``<template>``
- - The contents of the element aren't placed in the Element itself.
-   They are instead placed into a Fragment that you can obtain from
-   the element's "content" attribute.
-
-``<script>``
- - Blocks until all previous imports have been loaded, then loads the
-   library given in the script block, as described in
-   [scripts.md](scripts.md).
-
-``<style>``
- - Adds the contents to the module's styles.
-
-``<content>``
-``<content select="...">``
- - In a shadow tree, acts as an insertion point for distributed nodes.
-   The select="" attribute gives the selector to use to pick the nodes
-   to place in this insertion point; it defaults to everything.
-
-``<img src="foo.bin">``
- - Sky fetches the bits for foo.bin, looks for a decoder for those
-   bits, and renders the bits that the decoder returns.
-
-``<div>``
- - Element that does nothing.
-
-``<span>``
- - Element that does nothing.
-
-``<iframe src="foo.bin">``
- - Sky tells mojo to open an application for foo.bin, and hands that
-   application a view so that the application can render appropriately.
-
-``<t>``
- - Within a ``<t>`` section, whitespace is not trimmed from the start and
-   end of text nodes by the parser.
-   TOOD(ianh): figure out if the authoring aesthetics of this are ok
-
-``<a href="foo.bin">``
- - A widget that, when invoked, causes mojo to open a new application
-   for "foo.bin".
-
-``<title>``
- - Sets the contents as the application's title (as provided by Sky to
-   the view manager). (Actually just ensures that any time the element
-   is mutated, module.application.title is set to the element's
-   contents.)
-
-
-Sky Markup: Global Attributes
-=============================
-
-The following attributes are available on all elements:
-
-* ``id=""`` (any value)
-* ``class=""`` (any value, space-separated)
-* ``style=""`` (declaration part of a Sky style rule)
-* ``lang=""`` (language code)
-* ``dir=""`` (ltr or rtl only)
-* ``contenteditable=""`` (subject to future developments)
-* ``tabindex=""`` (subject to future developments)