Flesh out the speculative parser spec

whatwg · Oct 29, 2020 · 122cff2 · 122cff2
1 parent 0c4cb34
commit 122cff2
Showing 1 changed file with 125 additions and 12 deletions.
diff --git a/source b/source
@@ -111086,8 +111086,6 @@ document.body.appendChild(text);
       invocations of the tokenizer, yielding control back to the caller. (Tokenization will resume
       when the caller returns to the "outer" tree construction stage.)</p>
 
-      <p class="XXX">Speculatively parse the remainder of the document.write string here?</p>
-
       <p class="note">The tree construction stage of this particular parser is <a
       href="#nestedParsing">being called reentrantly</a>, say from a call to <code
       data-x="dom-document-write">document.write()</code>.</p>
@@ -112665,14 +112663,6 @@ document.body.appendChild(text);
 
   </div>
 
-  <div w-nodev>
-
-  <h4>Speculative HTML parsing</h4>
-
-  <p class="XXX"><dfn>Speculative HTML parser</dfn>, <dfn>start the speculative HTML parser</dfn>,
-  <dfn>stop the speculative HTML parser</dfn>...</p>
-
-  </div>
 
   <div w-nodev>
 
@@ -112797,8 +112787,7 @@ document.body.appendChild(text);
    <li><p>Throw away any pending content in the <span>input stream</span>, and discard any future
    content that would have been added to it.</p></li>
 
-   <li><p>If there is an active <span>speculative HTML parser</span>, <span>stop the speculative
-   HTML parser</span> for this HTML parser.</p></li>
+   <li><p><span>Stop the speculative HTML parser</span> for this HTML parser.</p></li>
 
    <li><p>Set the <span>current document readiness</span> to "<code data-x="">interactive</code>"<!--
    this immediately fires an event -->.</p></li>
@@ -112817,6 +112806,127 @@ document.body.appendChild(text);
   </div>
 
 
+  <div w-nodev>
+
+  <h4>Speculative HTML parsing</h4>
+
+  <p>User agents may implement an optimization, as described in this section, to speculatively fetch
+  resources that are declared in the HTML markup while the HTML parser is waiting for a
+  <span>pending parsing-blocking script</span> to be fetched and executed. While this optimization
+  is not defined in precise detail, there are some rules to consider for interoperability.</p>
+
+  <p>Each <span>HTML parser</span> can have an <dfn export>active speculative HTML parser</dfn>. It
+  is initially null.</p>
+
+  <p>The <dfn export>speculative HTML parser</dfn> must act like the normal HTML parser (e.g., the
+  tree builder rules apply), with some exceptions:</p>
+
+  <ul>
+   <li><p>Scripts must not be executed.</p></li>
+
+   <li><p>Character encoding declarations must be ignored.</p></li>
+
+   <li>
+    <p>The state of the normal HTML parser and the document itself must not be affected.</p>
+
+    <p class="example">For example, the <span>next input character</span> or the <span>stack of open
+    elements</span> for the normal HTML parser is not affected by the <span>speculative HTML
+    parser</span>.</p>
+   </li>
+
+   <li>
+    <p>The result of the speculative parsing is primarily a series of <span>speculative
+    fetches</span>. Which kinds of resources to speculatively fetch is
+    <span>implementation-defined</span>, but user agents must not speculatively fetch resources that
+    would not be fetched with the normal HTML parser, under the assumption that the script that is
+    blocking the HTML parser does nothing.</p>
+
+    <p class="note">It is possible that the same markup is seen multiple times from the
+    <span>speculative HTML parser</span> and then the normal HTML parser. It is expected that
+    duplicated fetches will be prevented by normal caching rules.</p>
+   </li>
+  </ul>
+
+  <p>The <dfn export>speculative fetches</dfn> must follow these rules:</p>
+
+  <p class="XXX">Should some of these things be applied to the document "for real", even
+  though they are found speculatively?</p>
+
+  <ul>
+   <li><p>Let the HTML parser's invocation of the <span data-x="concept-appcache-init">application
+   cache selection algorithm</span> complete before initiating any speculative fetches, if
+   applicable.</p></li>
+
+   <li>
+    <p>If the <span>speculative HTML parser</span> encounters one of the following elements, then
+    act as if that element is processed for the purpose of its effect of speculative fetches for
+    resources after the element.</p>
+
+    <ul class="brief">
+     <li>A <code>base</code> element.</li>
+
+     <li>A <code>meta</code> element whose <code data-x="attr-meta-http-equiv">http-equiv</code>
+     attribute is in the <span data-x="attr-meta-http-equiv-content-security-policy">Content
+     security policy</span> state.</li>
+
+     <li>A <code>meta</code> element whose <code data-x="attr-meta-name">name</code> attribute is an
+     <span>ASCII case-insensitive</span> match for "<code
+     data-x="meta-referrer">referrer</code>".</li>
+
+     <li>A <code>meta</code> element whose <code data-x="attr-meta-name">name</code> attribute is an
+     <span>ASCII case-insensitive</span> match for "<code data-x="">viewport</code>". (This can
+     affect whether a media query list <span>matches the environment</span>.) <ref
+     spec=CSSDEVICEADAPT></li>
+    </ul>
+   </li>
+  </ul>
+
+  <p>To <dfn>start the speculative HTML parser</dfn> for an instance of an HTML parser
+  <var>parser</var>:</p>
+
+  <ol>
+   <li><p>Optionally, return. (This allows user agents to opt out of speculative HTML
+   parsing.)</p></li>
+
+   <li>
+    <p>If <var>parser</var> already has an <span>active speculative HTML parser</span>, then
+    <span>stop the speculative HTML parser</span> for <var>parser</var>.</p>
+
+    <p class="note">This can happen when <code data-x="">document.write()</code> writes another
+    parser-blocking script. For simplicity, this specification always restarts speculative parsing,
+    but user agents can implement a more efficient strategy, so long as the end result is
+    equivalent.</p>
+   </li>
+
+   <li><p>Let <var>speculativeParser</var> be a new <span>speculative HTML parser</span>, with the
+   same state as <var>parser</var>.</p></li>
+
+   <li><p>Set <var>parser</var>'s <span>active speculative HTML parser</span> to
+   <var>speculativeParser</var>.</p></li>
+
+   <li><p><span>In parallel</span>, run <var>speculativeParser</var> until it is stopped or until it
+   reaches the end of its <span>input stream</span>.</p></li>
+  </ol>
+
+
+  <p>To <dfn>stop the speculative HTML parser</dfn> for an instance of an HTML parser
+  <var>parser</var>:</p>
+
+  <ol>
+   <li><p>Let <var>speculativeParser</var> be <var>parser</var>'s <span>active speculative HTML
+   parser</span>.</p></li>
+
+   <li><p>If <var>speculativeParser</var> is null, then return.</p></li>
+
+   <li><p>Throw away any pending content in <var>speculativeParser</var>'s <span>input
+   stream</span>, and discard any future content that would have been added to it.</p></li>
+
+   <li><p>Set <var>parser</var>'s <span>active speculative HTML parser</span> to null.</p></li>
+  </ol>
+
+  </div>
+
+
   <div w-nodev>
 
   <h4>Coercing an HTML DOM into an infoset</h4>
@@ -123986,6 +124096,9 @@ INSERT INTERFACES HERE
    <dt id="refsCSSCOLORADJUST">[CSSCOLORADJUST]</dt>
    <dd><cite><a href="https://drafts.csswg.org/css-color-adjust/">CSS Color Adjustment Module</a></cite>, E. Etemad, R. Atanassov, R. Lillesveen, T. Atkins. W3C.</dd>
 
+   <dt id="refsCSSDEVICEADAPT">[CSSDEVICEADAPT]</dt>
+   <dd><cite><a href="https://drafts.csswg.org/ccss-device-adapt/">CSS Device Adaption</a></cite>, F. Rivoal, M. Rakow. W3C.</dd>
+
    <dt id="refsCSSDISPLAY">[CSSDISPLAY]</dt>
    <dd><cite><a href="https://drafts.csswg.org/css-display/">CSS Display</a></cite>, T. Atkins, E. Etemad. W3C.</dd>