Whitespace changes in navigation for 4.7

In [38523] the argument item_spacing was introduced for the functions wp_nav_menu(), wp_list_pages(), and wp_page_menu() to:

• ensure whitespace equivalent output when wp_nav_menu() falls back to wp_list_pages(), and,
• allow theme authors to control how whitespace is output.

Backward compatibility changes.

There is a backward compatibility breakage when wp_nav_menu() is empty and falls back to using wp_list_pages().

By default, wp_nav_menu() outputs markup with whitespace between each list item (</li> <li>). Prior to WordPress 4.7 when falling back to wp_list_pages() there would be no whitespace between list items (</li><li>). This caused layout to change when certain styles were applied.

From WordPress 4.7 onward when falling back to a page list, wp_nav_menu() will output markup with whitespace between each list item.

There is no change to the default behaviour when calling wp_list_pages() directly, it will not have any whitespace between each item in the menu.

Controlling how menus and page lists output whitespace.

From WordPress 4.7 onwards, theme authors will be able to control whether whitespace in wp_nav_menu(), wp_list_pages() and wp_page_menu() with the item_spacing argument.

The item_spacing argument accepts either preserve or discard. To discard the whitespace in a menu, call the function with:

wp_nav_menu( array(
	'theme_location' => 'top',
	'menu_id'        => 'top-menu',
	'item_spacing'   => 'discard', // default 'preserve'
) );

The same argument can be used for wp_list_pages(), and wp_page_menu() although the default is discard.

#4-7, #dev-notes, #menus