The HTML5 parsing algorithm is meant to demystify HTML parsing and make it uniform across implementations in a backwards-compatible way. The algorithm has had “in the lab” testing, but so far it hasn’t been tested inside a browser by a large number of people. You can help change that now!
A while ago, an implementation of the HTML5 parsing algorithm landed on mozilla-central preffed off. Anyone who is testing Firefox nightly builds can now opt to turn on the HTML5 parser and test it.
First, this isn’t release-quality software. Testing the HTML5 parser carries all the same risks as testing a nightly build in general, and then some. It may crash, it may corrupt your Firefox profile, etc. If you aren’t comfortable with taking the risks associated with running nighly builds, you shouldn’t participate.
If you are still comfortable with testing, download a trunk
build, run it, navigate to
about:config and flip the
makes Gecko use the HTML5 parser when loading pages into the content
area and when setting
innerHTML. The HTML5 parser is not
used for HTML embedded in feeds, Netscape bookmark import, View
Source, etc., yet.
html5.enable preference doesn’t require a
restart to take effect. It takes effect the next time you load a
The main thing is getting the HTML5 parser exposed to a wide range of real Web content that people browse. This may turn up crashes or compatibility problems.
So the way to help is to use nightly builds with the HTML5 parser for browsing as usual. If you see no difference, things are going well! If you see a page misbehaving—or, worse, crashing—with the HTML5 parser turned on but not with it turned off, please report the problem.
Please file bugs in the “Core” product under “HTML: Parser” component with “[HTML5] ” at the start of the summary.
First and foremost, please refer to the list of known bugs.
However, I’d like to highlight a particular issue: Support for
comments ending with
--!> is in the spec, but the
hasn’t landed, yet. Support for similar endings of
pseudo-comment escapes within
script element content is
the spec yet. The practical effect is that the rest of the page
may end up being swallowed up inside a comment or a
Another issue is that the new parser doesn’t yet inhibit
document.write() in places where it shouldn’t be
allowed per spec but where the old parser allowed it.
So what’s fun if success is that you notice no change? There are important technical things under the hood—like TCP packet boundaries not affecting the parse result and there never being unnotified nodes in the tree when the event loop spins—but you aren’t supposed to notice.
However, there is a major new visible feature, too. With the HTML5
parser, you can use SVG and MathML in
This means that you can:
Use SVG graphics inline without having to change your HTML content to work with XML parsing and without having to develop an alternative page for IE.
Use properly laid out math without having to change your HTML content to work with XML parsing.
And yes, you can even put SVG inside MathML
or MathML inside
<foreignObject>. The mixing
you’ve seen in XML is now supported in HTML, too.
If you aren’t concerned with taking the steps to make things
degrade nicely in browsers that don’t support SVG and MathML in
HTML, you can simply copy and paste XML output from your favorite SVG
or MathML editor into your HTML source as long as the editor doesn’t
use namespace prefixes for elements and uses the prefix
for XLink attributes.
If you don’t use the XML empty element syntax and you put you
SVG text nodes in CDATA sections, the page will degrade gracefully in
older HTML browser so that the image simply disappears but the rest
of the page is intact. You can even put a fallback bitmap as
<desc>. Unfortunately, there isn’t a
similar technique for MathML, though if you want to develop one, I
suggest experimenting with the
There are known issues with matching camelCase names with