Hi,
The documentation page seem you reference appears to be complete to me. I’m not the writer or maintainer of the documentation but the section you mention I think is just supposed to be an example of how the gallery field might be used it use a standard WP gallery shortcode and I think that you are supposed to see the WordPress Codex page on the galley shortcode tag for more information. https://codex.wordpress.org/Gallery_Shortcode
Can you elaborate on what you feel is missing?
