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Maybe xdotool [0] is what you're looking for.

[0] https://github.com/jordansissel/xdotool/

XML interfaces are common in toolkits, look at Guile for GTK or Qt Quick/QML. One of the ancient X window toolkits was the Athena widget set (baked in most X servers, https://www.x.org/releases/X11R7.7/doc/libXaw/libXaw.html). I don't know from XML interface to design Athena GUIs.

dtksh did that, more or less. not with xml.

https://www.brendangregg.com/dtkshdemos.html

You might want to check dbus… most desktop applications have a dbus interface. I normally use qdbus from command line.