Would you mind explaining exactly what the \z and x are doing in the regex?

Sure, to quote the docs

\z Match only at end of string

This is very similar to $ except $ matches the end of a line or before a newline.

x Extend your pattern's legibility by permitting whitespace and comments.

As it says, it allows for more readable regex, which is generally desirable considering the acute succinctness of regular expressions.
HTH

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broquaint