Add initial insertion mode errors (#19)

* Add initial insertion mode errors

* Fix review nits

Author: inikulin

source

@@ -100157,6 +100157,15 @@ dictionary <dfn>StorageEventInit</dfn> : <span>EventInit</span> {
      Such <span data-x="code point">code points</span> are parsed as-is and usually, where parsing
      rules don't apply any additional restrictions, make their way into the DOM.</p>
 
+    <tr>
+     <td><dfn data-x="parse-error-non-conforming-doctype">non-conforming-doctype</dfn>
+     <td><p>This error occurs if the parser encounters the <span
+     data-x="syntax-doctype">DOCTYPE</span> correctly placed as a document preamble and other than
+     <code data-x="">&lt;!DOCTYPE html></code> or <code data-x="">&lt;!DOCTYPE html SYSTEM
+     "about:legacy-compat"></code>. For <a href="#quirks-mode-doctypes">some non-conforming
+     DOCTYPEs</a> the parser sets the <code>Document</code> to <span>quirks mode</span> or
+     <span>limited-quirks mode</span>.</p>
+
     <tr>
      <td><dfn data-x="parse-error-non-void-html-element-start-tag-with-trailing-solidus">non-void-html-element-start-tag-with-trailing-solidus</dfn>
      <td>
@@ -100262,6 +100271,15 @@ dictionary <dfn>StorageEventInit</dfn> : <span>EventInit</span> {
        data-x="">foo</code>" attribute to "<code data-x="">b'ar'</code>".</p>
      </div>
 
+    <tr>
+      <td><dfn data-x="parse-error-missing-doctype">missing-doctype</dfn>
+      <td>
+        <p>This error occurs if the parser encounters any content other than <span
+        data-x="syntax-comments">comments</span> or <span>ASCII whitespace</span> before <span
+        data-x="syntax-doctype">DOCTYPE</span> at the beginning of the document, i.e. DOCTYPE is not
+        a document preamble. In this case the parser sets the <code>Document</code> to <span>quirks
+        mode</span>.</p>
+
     <tr>
      <td><dfn data-x="parse-error-unexpected-equals-sign-before-attribute-name">unexpected-equals-sign-before-attribute-name</dfn>
      <td>
@@ -105037,7 +105055,9 @@ document.body.appendChild(text);
     <p>If the DOCTYPE token's name is not a <span>case-sensitive</span> match for the string "<code
     data-x="">html</code>", or the token's public identifier is not missing, or the token's system
     identifier is neither missing nor a <span>case-sensitive</span> match for the string
-    "<code>about:legacy-compat</code>", then there is a <span>parse error</span>.</p>
+    "<code>about:legacy-compat</code>", then this is a <span
+    data-x="parse-error-non-conforming-doctype">non-conforming-doctype</span> <span>parse
+    error</span>.</p>
 
     <p>Append a <code>DocumentType</code> node to the <code>Document</code> node, with the <code
     data-x="">name</code> attribute set to the name given in the DOCTYPE token, or the empty string
@@ -105147,8 +105167,9 @@ document.body.appendChild(text);
    <dd>
 
     <p>If the document is <em>not</em> <span>an <code>iframe</code> <code
-    data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, then this is a <span>parse
-    error</span>; set the <code>Document</code> to <span>quirks mode</span>.</p>
+    data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, then this is a <span
+    data-x="parse-error-missing-doctype">missing-doctype</span> <span>parse error</span>; set the
+    <code>Document</code> to <span>quirks mode</span>.</p>
 
     <p>In any case, switch the <span>insertion mode</span> to "<span data-x="insertion mode: before
     html">before html</span>", then reprocess the token.</p>