Mouse keys

Windows has since long had the accessibility feature known as Mouse Keys, which allows the user to move the mouse pointer and simulate mouse clicks using the numeric keypad keys. This Wikipedia article offers more perspective on the history of this feature, from its inception on Unix-driven X Window graphical terminal, to its adoption in mass-market Windows and Apple OS X.

A less known fact about the Mouse Keys under Windows is that the keys used for specific mouse key functions (mouse left/right, button up/down, etc) are customisable.

Even though mouse key customisation is not (yet!) supported by KbdEdit, a major change since version 18.9.0 is that any such customisations present in the original layout are now being preserved in any cusom layouts based on it.

Mouse Key functions in the UI

Additionally, since KbdEdit 18.9.0 the low level editor UI shows details of all mouse key functions supported by the current layout.

Any key with a mouse key function is visually denoted by a small grey mark in the lower right corner, with the mouse hover tooltip showing the actual function:

Default Mouse Key mappings

The vast majority of the standard keyboard layouts supplied in current Windows versions use the default mouse key mappings listed below:

Mouse Key function	Default VK code	Corresponding numpad key
Active Button Click	VK_CLEAR	digit 5
Up Right	VK_PRIOR	digit 9
Down Right	VK_NEXT	digit 3
Down Left	VK_END	digit 1
Up Left	VK_HOME	digit 7
Left	VK_LEFT	digit 4
Up	VK_UP	digit 8
Right	VK_RIGHT	digit 6
Down	VK_DOWN	digit 2
Active Button Down	VK_INSERT	digit 0
Active Button Up	VK_DELETE	. (decimal point)
Select Both Buttons	VK_MULTIPLY	* (star)
Active Button Double Click	VK_ADD	+ (plus sign)
Select Right Button	VK_SUBTRACT	- (minus sign)
Select Left Button	VK_DIVIDE	/ (division)
Toggle Mouse Keys	VK_NUMLOCK	numlock key

The only system layouts deviating from these standard mappings are the exotic "NEC" Japanese keyboards (kbdnec.dll, kbdnec95.dll, kbdnecat.dll, kbdnecnt.dll).