Function: x-select-text

Select TEXT, a string, according to the window system.

On X, if `x-select-enable-clipboard' is non-nil, copy TEXT to the
clipboard. If `x-select-enable-primary' is non-nil, put TEXT in
the primary selection.

On MS-Windows, make TEXT the current selection. If
`x-select-enable-clipboard' is non-nil, copy the text to the
clipboard as well.

On Nextstep, put TEXT in the pasteboard (`x-select-enable-clipboard' is not used).