A key should contain an English letter, or a digit, or 2/3-digit key-code used by browser's keydown events, or a predifined flag such as HOME, DOWN, UPARROW, etc. Example, the "065" or "65" is the same as "A", the "040" is down-arrow key, and the "113" is "F2" key. In case of multiple keys, values should be separated by the "," (coma) character. Example: "B,2,191" means that "B", "2" and "?" keyboard keys will trigger drop down action. Each value may contain optional modifiers such as Shift, Ctrl or Alt with optional + or space separator. Example: "Shift+A,Up Ctrl,Shift+Space,F2".
All entries are case insensitive and suffix "Arrow" is optional for "Up/Down/Left/Right" arrow keys.
Notes: This property has effect regardless of visibility of custom button.
In case of modifiers and some of F# keys, a browser may override key event and drop-down action may fail.
Different browsers may have different codes for same keys. For example: key-code of "+" in IE is 181, but in Firefox it is 107.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2