A small comment for anyone new to xslt. The author references a wildcard rule in the comments [0]. While that is true, they are calling an identity transformation [1]. Identity transformations are very common in xslt.

[0] https://github.com/Evidlo/xsl-website/blob/0dda1d82ce1eb01b7... [1] https://en.wikipedia.org/wiki/Identity_transform