Current X position of the cursor when the event fired, relative to the upper-left corner of the window, reported in pixels. (0, 0) is the upper left, (window.width - 1, window.height - 1) is the lower right corner of the window.
The D Programming Language's Unofficial Docs
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Current X position of the cursor when the event fired, relative to the upper-left corner of the window, reported in pixels. (0, 0) is the upper left, (window.width - 1, window.height - 1) is the lower right corner of the window.