THANKS Head_on_a_Stick!!! 

Why this error message?

Because you used a capital X in the geometry specification, try it again with a lower case x instead.

I was playing XMahJongg these days and I have a couple of questions.
Not important ones though, I'm asking just out of curiosity:

1) Launching XMahJongg (from console) with the geometry argument (in order to fit the screen), like this "xmahjongg -g 1360X768", produces the error message "xmahjongg: warning: bad geometry specification". 

Not any visible side-effects though. The game runs properly.

Why this error message? Running xrandr returns this mode as the active one: "1360x768_60.00  60.00".

2) Looking at it's source code, one can see (giving "./configure -h") a possible arguments for configure: "--with-x   use the X Window System".

Any idea, what it does???

Is anyone familiar with these X related things?
TIA!!!