def scroll_page_up(event):
    """
    Scroll page up. (Prefer the cursor at the bottom of the page, after scrolling.)
    """
    w = event.app.layout.current_window
    b = event.app.current_buffer
    if w and w.render_info:
        line_index = max(0, min(w.render_info.first_visible_line(), b.
            document.cursor_position_row - 1))
        b.cursor_position = b.document.translate_row_col_to_index(line_index, 0
            )
        b.cursor_position += b.document.get_start_of_line_position(
            after_whitespace=True)
        w.vertical_scroll = 0
