https://issues.chromium.org/issues/451401343 tracks work needed in the upstream xml-rs repository, so it seems like the team is working on addressing issues that would affect standards compliance.
Disclaimer: I work on Chrome and have occasionally dabbled in libxml2/libxslt in the past, but I'm not directly involved in any of the current work.
It's one thing if the library was proactively written with ABI compatibility in mind. It's another thing entirely if the library happens to expose all its implementation details in the headers, making it that much harder to change things.
Disclaimer: I work on Chrome/Blink and I've also contributed a (very small) number of patches to libxml/libxslt.
It's not just a matter of replacing the libxslt; libxslt integrates quite closely with libxml2. There's a fair amount of glue to bolt libxml2/libxslt on to Blink (and WebKit); I can't speak for Gecko.
Even when there's no work on new XML/XSLT features, there's a passive cost to just having that glue code around since it adds quirks and special cases that otherwise wouldn't exist.
Disclaimer: I work on Chrome and I have contributed a (very) small number of fixes to libxml2/libxslt for some of the recent security bugs.
Speaking from personal experience, working on libxslt... not easy for many reasons beyond the complexity of XSLT itself. For instance:
- libxslt is linked against by all sorts of random apps and changes to libxslt (and libxml2) must not break ABI compatibility. This often constrains the shape of possible patches, and makes it that much harder to write systemic fixes.
- libxslt reaches into libxml and reuses fields in creative ways, e.g. libxml2's `xmlDoc` has a `compression` field that is ostensibly for storing the zlib compression level [1], but libxslt has co-opted it for a completely different purpose [2].
- There's a lot of missing institutional knowledge and no clear place to go for answers, e.g. what does a compile-time flag that guards "refactored parts of libxslt" [3] do exactly?
At least some of the implementation complexity is already there under the hood. WebKit/Blink have an optimization to use 8-bit characters for strings that consist only of latin1 characters.
A large part of the problem is the legacy burden of libxml2 and libxslt. A lot of the implementation details are exposed in headers, and that makes it hard to write improvements/fixes that don't break ABI compatibility.
> Do they distrust their own coders to the same degree they distrust the processes they sandbox? I suspect the answer to this is "no" but I would like to hear from someone who actually codes there.
Actually, the answer is yes. That's why the renderer process is sandboxed.
Disclaimer: I work on Chrome and have occasionally dabbled in libxml2/libxslt in the past, but I'm not directly involved in any of the current work.