Function paste_button 

pub fn paste_button(
    kinds: &[ContentType],
    paste: impl Fn(&[ItemProvider]) + 'static,
) -> ViewHandle

PasteButton(supportedContentTypes:payloadAction:) — a button that pastes.

Not generic: its label is fixed, so there is no content type to pass. What arrives in the action is the pasteboard’s item providers, the same shape on_paste_command receives.