The keyboard widget allows ActionWidgets to be triggered by specific key combinations. There is also a shorthand for generating [[Messages]] via the `message` and `param` attributes.
Key strings are made up of one or more key specifiers separated by spaces. Each key specifier is zero or more of the modifiers <kbd>alt</kbd>, <kbd>shift</kbd>, <kbd>ctrl</kbd> or <kbd>meta</kbd> followed by the name of a key, all joined with "+" plus or "-" minus symbols. Key names are either the letter or digit printed on the key (eg "a" or "1"), or one of the special keys <kbd>backspace</kbd>, <kbd>tab</kbd>, <kbd>enter</kbd> or <kbd>escape</kbd>.