Not so fast, Martin...
At one time I was able to extrude up to a plane or planar face, then the second direction could also be positive up to another plane or planar face.
his leaves the sketch completely outside of the created feature.
Not sure if it was a bug or intended behavior. I am not sure what the limitations are, but I found it interesting at the time.
I haven't found it useful enough (read: too limited) to explore it much further.
edit: one limitation: you cannot add taper to the extrude.
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