This function is to add a sub-item to an existing item in the admin panels nav bar.
| Parameter | Details |
|---|---|
| $parent_slug | (string) The slug name for the parent menu (or the file name of a standard WordPress admin page). |
| $page_title | (string) The text to be displayed in the title tags of the page when the menu is selected. |
| $menu_title | (string) The text to be used for the menu. |
| $capability | (string) The capability required for this menu to be displayed to the user. |
| $menu_slug | (string) The slug name to refer to this menu by (should be unique for this menu). |
| $function | (callable) (Optional) The function to be called to output the content for this page. |
Here are a list of slugs for $parent_slug