There is currently discussion in WHATWG regarding the potential removal of XSLT from the HTML standard. This is relevant to XDoc since the core of the web viewer is powered by XSLT: it is what handles turning the preprocessed XDoc markup language into valid HTML, which is then inserted into the page by the web viewer.

It is unclear if the XSLT removal will go through or not, but there does appear to be at least moderate support by browser developers (the author of the issue is a Chromium dev, and a person who does web standards work at Apple stated cautious support on behalf of WebKit). Once XSLT is removed from the standard, it would be up to each browser whether or not to keep XSLT support.

We have several options in the event that XSLT is removed from browsers. The easiest is to use a JavaScript polyfill library to provide the XSLT functionality that is being removed. We could also investigate the use of alternative libraries for XML transformation, or even consider something like pre-compiling the XDoc markup language as part of the processing that occurs when the xdata and xindex files are generated.