KEY
Underlines a character of the TITLE of a menu item or submenu. Pressing that character while the parent menu is open activates the item. For a submenu in the menu bar, Alt+character opens it from any control in the dialog. Same as writing "&" before that character in TITLE, see IupMenuItem. Deprecated, use the "&" in TITLE.
Not supported in Cocoa, EFL, Android and iOS. In Haiku the underline and the key are active when the system menu preference shows triggers, and Alt+character does not open a menu bar submenu.
Value
A single character. The first occurrence of it in TITLE is underlined. When the character is not in TITLE nothing is underlined.
Default: NULL
Notes
It is applied when TITLE is set. After mapping, a new KEY takes effect when TITLE is set again.