XOR cursor is not supported in X11

In QCursor document, we say that:
The cursor bitmap (B) and mask (M) bits are combined like this:
B=1 and M=1 gives black.
B=0 and M=1 gives white.
B=0 and M=0 gives transparent.
B=1 and M=0 gives an XOR'd result.

But actually the XOR cursor is only supported in Windows. Qt-x11 doesn't support this. Other platform not tested
Please change the document.