No highlighting on some xsl files

[jjrsylvestre]

I'm using Zed 0.161.2 on Archlinux.

When opening a few of the xsl files in this project:
https://github.com/PreTeXtBook/pretext/tree/master/xsl
I get no syntax highlighting.

Most of the xsl files in the linked directory above open fine with syntax highlighted, but
pretext-common.xsl
pretext-html.xsl
pretext-latex.xsl
open with no highlighting.

Screenshot:

[sweetppro]

interesting,
if I take out the <xsl:stylesheet> node, highlighting works

[jjrsylvestre]

If I take out the <xsl:stylesheet> node, the document gets only partially highlighted.

Screenshot of pretext-html.xsl with <xsl:stylesheet> node removed: