Re: [whatwg/dom] Define processing instruction attributes (PR #1454)

@foolip commented on this pull request.



> +
+<div algorithm>
+<p>The <dfn method for=ProcessingInstruction><code>hasAttribute(<var>name</var>)</code></dfn>
+method steps are:
+
+<ol>
+ <li><p>If <a>this</a>'s <a for=Node>node document</a> is an <a>HTML document</a>, then set
+ <var>name</var> to <var>name</var> in <a>ASCII lowercase</a>.
+
+ <li><p>Return true if <a>this</a>'s <a for=ProcessingInstruction>attribute map</a>[<var>name</var>]
+ <a for=set>exists</a>; otherwise false.
+</ol>
+</div>
+
+<div algorithm>
+<p>To <dfn>update attributes from data</dfn> for a {{ProcessingInstruction}} <a for=/>node</a> <var>pi</var>:

Yes, it was based on how this works in Chromium:

https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/dom/processing_instruction.cc;l=120-146;drc=bc971aee7d328d1e886ba76adc540805ea480981

In WebKit it is similar:

https://github.com/WebKit/WebKit/blob/9af8ffff919a1a1478b8a43cef821adb49a4e6a1/Source/WebCore/dom/ProcessingInstruction.cpp#L99
https://github.com/WebKit/WebKit/blob/26d7991c939a41bbab5d01263900598b67220208/Source/WebCore/xml/parser/XMLDocumentParserLibxml2.cpp#L1556-L1574

In Gecko it's a little bit different, every attribute lookup uses an attribute parser and I can't tell if it exactly matches XML or not:
https://github.com/mozilla-firefox/firefox/blob/22d04b52b0eb8d9fa11bf8ede5ccc0243a07c5ba/dom/xml/XMLStylesheetProcessingInstruction.cpp#L92
https://github.com/mozilla-firefox/firefox/blob/afe51e48c9deecccbaf64a74d6f207456433df98/dom/xml/ProcessingInstruction.cpp#L77
https://github.com/mozilla-firefox/firefox/blob/22d04b52b0eb8d9fa11bf8ede5ccc0243a07c5ba/dom/base/nsContentUtils.cpp#L1842-L1943

The difference from what's already implemented is that we'd use the HTML parser in HTML documents, instead of unconditionally using the XML parser.

For compat, this difference means that existing content that creates a `<?xml-stylesheet href="..."?>` PI and moves it to an HTML document would take the HTML parser path instead of XML. For that to make a difference, I think that content would need to be invalid XML attribute syntax (like `<?xml-stylesheet href='...'?>`) and depends on it being broken (doing nothing) when being moved to HTML.

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