Improve some `post_status`-related documentation.

Props ericlewis.
See #30230.

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Display error message when Media Library upload fails.

Props gcorne.
Fixes #29891.

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Check `$_current_page` before using it in `Walker_Page->start_el()`.

Props jeremyfelt.
Fixes #26901.

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All duplicate slugs across different post types.

Adds unit test.

Props mboynes, nacin.
Fixes #18962.

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Allow `get_pages()`, with `child_of` passed to it, to work with interrupted hierarchies.

Adds unit test.
Fixes #18962.

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Remove failing unit test after [30090].

Fixes #30194.

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In `gallery_shortcode()`, when the `link` attribute is equal to `file`, make sure to pass `$attr` as the 6th (!) argument, not 5th, to `wp_get_attachment_link()`.

Props bradyvercher.
Fixes #27402.

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In `_wp_json_convert_string()`, when `$use_mb` is `false`, perhaps pass a variable that actually exists to `wp_check_invalid_utf8()`.

Introduced in [30055].
See #30224.

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In `WP_Meta_Query->get_sql_for_clause()`, the empty initialization of `$where` is dead code and can be removed.

See #30224.

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In `customize.php`, check that `$autofocus` is an `array` after running `wp_unslash()` instead of before. This is admittedly to skip a traversable hint in Scrutinizer.

See #30224.

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Make the docs type for `return` in `wpmu_create_user()` more specific.

See #30224.

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In `get_the_pagination()`, don't pass `$links` to `_navigation_markup()` if it is not a string - `paginate_links()` can return an `array`.

See #30224.

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In `wp_ajax_ajax_tag_search()`, bail immediately if `$_GET['tax']` isn't set so that all of the variable setting can happen in the same nest scope as the rest of the function - `wp_die()` confuses Scrutinizer.

See #30224.

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In `wp_ajax_get_tagcloud()`, bail immediately if `$_POST['tax']` isn't set so that all of the variable setting can happen in the same nest scope as the rest of the function - `wp_die()` confuses Scrutinizer.

See #30224.

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Fix the return value doc for `WP_List_Table->get_pagination_arg()`.

See #30224.

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Declare the `$options` property for `WP_Upgrader_Skin`.

See #30224.

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Declare the `$update_count` and `$update_current` properties for `WP_Upgrader`.

See #30224.

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Declare the `$uploaded_headers` and `$default_headers` properties for `WP_Customize_Header_Image_Control`.

See #30224.

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In `_WP_Editors::editor_settings()`, `$str1` and `$str2` don't need to be initialized empty.

See #30224.

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Split tests for wp_get_sites()

Test various arguments for `wp_get_sites()` in a more intentful way rather than in one large test. Leave tests for limit and offset together for convenience.

See #30080

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