How do I find out who requested a port?

[Michael]

How do I find out which port requested another port?

Specifically, lets say I'd rather have quartz-based, rather than x11-based, ports installed.

Attempting to install gtk3 -x11 +quartz gave me the error message that gdk-pixbuf2 must be installed without +x11.

So I've got X11 installed, without realizing it, and without wanting it.
How would I go about tracing down all the ports that I'd need to re-install without X11?

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