A visual form component - button. Can be created with a direct constructor, or calling a function <b>New_button</b>. It is intended to provide pressing it by a user. A handler of a click event - a method <b>click</b> of a parent form. Also other mouse or keyboard events are possible. To switch a button to an unavailable (grayed) or hidden state, use form events <grayed</b> / <b>hidden</b> (a button should be listed in a correspondent form's list <b>grayable[]</b> / <b>can_hide[]</b>).