diff --git a/wp-admin/edit-comments.php b/wp-admin/edit-comments.php
index c2a16eef0b..0dde8df01a 100644
--- a/wp-admin/edit-comments.php
+++ b/wp-admin/edit-comments.php
@@ -120,7 +120,7 @@ if ( $doaction ) {
 		$redirect_to = add_query_arg( 'deleted', $deleted, $redirect_to );
 	}
 	if ( $trashed || $spammed ) {
-		$redirect_to = add_query_arg( 'ids', join( ',', $comment_ids ), $redirect_to );
+		$redirect_to = add_query_arg( 'ids', implode( ',', $comment_ids ), $redirect_to );
 	}
 
 	wp_safe_redirect( $redirect_to );
diff --git a/wp-admin/edit.php b/wp-admin/edit.php
index bf54037451..40bc41c512 100644
--- a/wp-admin/edit.php
+++ b/wp-admin/edit.php
@@ -126,7 +126,7 @@ if ( $doaction ) {
 			$sendback = add_query_arg(
 				array(
 					'trashed' => $trashed,
-					'ids'     => join( ',', $post_ids ),
+					'ids'     => implode( ',', $post_ids ),
 					'locked'  => $locked,
 				),
 				$sendback
@@ -442,7 +442,7 @@ foreach ( $bulk_counts as $message => $count ) {
 }
 
 if ( $messages ) {
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . join( ' ', $messages ) . '</p></div>';
+	echo '<div id="message" class="updated notice is-dismissible"><p>' . implode( ' ', $messages ) . '</p></div>';
 }
 unset( $messages );
 
diff --git a/wp-admin/includes/ajax-actions.php b/wp-admin/includes/ajax-actions.php
index f359732b15..6ff2d2d9fd 100644
--- a/wp-admin/includes/ajax-actions.php
+++ b/wp-admin/includes/ajax-actions.php
@@ -162,7 +162,7 @@ function wp_ajax_ajax_tag_search() {
 		)
 	);
 
-	echo join( "\n", $results );
+	echo implode( "\n", $results );
 	wp_die();
 }
 
diff --git a/wp-admin/includes/class-wp-comments-list-table.php b/wp-admin/includes/class-wp-comments-list-table.php
index 1c7ac384ae..563187ffe4 100644
--- a/wp-admin/includes/class-wp-comments-list-table.php
+++ b/wp-admin/includes/class-wp-comments-list-table.php
@@ -615,7 +615,7 @@ class WP_Comments_List_Table extends WP_List_Table {
 		if ( ! $the_comment_class ) {
 			$the_comment_class = '';
 		}
-		$the_comment_class = join( ' ', get_comment_class( $the_comment_class, $comment, $comment->comment_post_ID ) );
+		$the_comment_class = implode( ' ', get_comment_class( $the_comment_class, $comment, $comment->comment_post_ID ) );
 
 		if ( $comment->comment_post_ID > 0 ) {
 			$post = get_post( $comment->comment_post_ID );
diff --git a/wp-admin/includes/class-wp-importer.php b/wp-admin/includes/class-wp-importer.php
index b60c783c90..d189061d5b 100644
--- a/wp-admin/includes/class-wp-importer.php
+++ b/wp-admin/includes/class-wp-importer.php
@@ -291,7 +291,7 @@ function get_cli_args( $param, $required = false ) {
 	$last_arg = null;
 	$return   = null;
 
-	$il = sizeof( $args );
+	$il = count( $args );
 
 	for ( $i = 1, $il; $i < $il; $i++ ) {
 		if ( (bool) preg_match( '/^--(.+)/', $args[ $i ], $match ) ) {
diff --git a/wp-admin/includes/class-wp-list-table.php b/wp-admin/includes/class-wp-list-table.php
index 2ef5f8d1b9..58d1cf9889 100644
--- a/wp-admin/includes/class-wp-list-table.php
+++ b/wp-admin/includes/class-wp-list-table.php
@@ -976,7 +976,7 @@ class WP_List_Table {
 		if ( ! empty( $infinite_scroll ) ) {
 			$pagination_links_class .= ' hide-if-js';
 		}
-		$output .= "\n<span class='$pagination_links_class'>" . join( "\n", $page_links ) . '</span>';
+		$output .= "\n<span class='$pagination_links_class'>" . implode( "\n", $page_links ) . '</span>';
 
 		if ( $total_pages ) {
 			$page_class = $total_pages < 2 ? ' one-page' : '';
@@ -1242,7 +1242,7 @@ class WP_List_Table {
 			$id    = $with_id ? "id='$column_key'" : '';
 
 			if ( ! empty( $class ) ) {
-				$class = "class='" . join( ' ', $class ) . "'";
+				$class = "class='" . implode( ' ', $class ) . "'";
 			}
 
 			echo "<$tag $scope $id $class>$column_display_name</$tag>";
diff --git a/wp-admin/includes/class-wp-media-list-table.php b/wp-admin/includes/class-wp-media-list-table.php
index e5988ed3c9..031f306987 100644
--- a/wp-admin/includes/class-wp-media-list-table.php
+++ b/wp-admin/includes/class-wp-media-list-table.php
@@ -614,7 +614,7 @@ class WP_Media_List_Table extends WP_List_Table {
 					);
 				}
 				/* translators: Used between list items, there is a space after the comma. */
-				echo join( __( ', ' ), $out );
+				echo implode( __( ', ' ), $out );
 			} else {
 				echo '<span aria-hidden="true">&#8212;</span><span class="screen-reader-text">' . get_taxonomy( $taxonomy )->labels->no_terms . '</span>';
 			}
diff --git a/wp-admin/includes/class-wp-posts-list-table.php b/wp-admin/includes/class-wp-posts-list-table.php
index 08e2ff58ec..67e7a279d4 100644
--- a/wp-admin/includes/class-wp-posts-list-table.php
+++ b/wp-admin/includes/class-wp-posts-list-table.php
@@ -1219,7 +1219,7 @@ class WP_Posts_List_Table extends WP_List_Table {
 				$term_links = apply_filters( 'post_column_taxonomy_links', $term_links, $taxonomy, $terms );
 
 				/* translators: Used between list items, there is a space after the comma. */
-				echo join( __( ', ' ), $term_links );
+				echo implode( __( ', ' ), $term_links );
 			} else {
 				echo '<span aria-hidden="true">&#8212;</span><span class="screen-reader-text">' . $taxonomy_object->labels->no_terms . '</span>';
 			}
diff --git a/wp-admin/includes/class-wp-site-health.php b/wp-admin/includes/class-wp-site-health.php
index 6070a57b9b..aa9d794095 100644
--- a/wp-admin/includes/class-wp-site-health.php
+++ b/wp-admin/includes/class-wp-site-health.php
@@ -1855,7 +1855,7 @@ class WP_Site_Health {
 			$hosts = explode( ',', WP_ACCESSIBLE_HOSTS );
 		}
 
-		if ( $blocked && 0 === sizeof( $hosts ) ) {
+		if ( $blocked && 0 === count( $hosts ) ) {
 			$result['status'] = 'critical';
 
 			$result['label'] = __( 'HTTP requests are blocked' );
@@ -1870,7 +1870,7 @@ class WP_Site_Health {
 			);
 		}
 
-		if ( $blocked && 0 < sizeof( $hosts ) ) {
+		if ( $blocked && 0 < count( $hosts ) ) {
 			$result['status'] = 'recommended';
 
 			$result['label'] = __( 'HTTP requests are partially blocked' );
diff --git a/wp-admin/includes/export.php b/wp-admin/includes/export.php
index 03b7f4ccfa..74d7c5f823 100644
--- a/wp-admin/includes/export.php
+++ b/wp-admin/includes/export.php
@@ -534,7 +534,7 @@ function export_wp( $args = array() ) {
 
 		// Fetch 20 posts at a time rather than loading the entire table into memory.
 		while ( $next_posts = array_splice( $post_ids, 0, 20 ) ) {
-			$where = 'WHERE ID IN (' . join( ',', $next_posts ) . ')';
+			$where = 'WHERE ID IN (' . implode( ',', $next_posts ) . ')';
 			$posts = $wpdb->get_results( "SELECT * FROM {$wpdb->posts} $where" );
 
 			// Begin Loop.
diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index 88ac0cae2f..cfb40529a6 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -489,7 +489,7 @@ function wp_edit_theme_plugin_file( $args ) {
 
 	$previous_content = file_get_contents( $real_file );
 
-	if ( ! is_writeable( $real_file ) ) {
+	if ( ! is_writable( $real_file ) ) {
 		return new WP_Error( 'file_not_writable' );
 	}
 
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index b23900961a..e2f21426dd 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -1118,7 +1118,7 @@ function image_align_input_fields( $post, $checked = '' ) {
 			" /><label for='image-align-{$name}-{$post->ID}' class='align image-align-{$name}-label'>$label</label>";
 	}
 
-	return join( "\n", $out );
+	return implode( "\n", $out );
 }
 
 /**
@@ -1195,7 +1195,7 @@ function image_size_input_fields( $post, $check = '' ) {
 	return array(
 		'label' => __( 'Size' ),
 		'input' => 'html',
-		'html'  => join( "\n", $out ),
+		'html'  => implode( "\n", $out ),
 	);
 }
 
@@ -1424,7 +1424,7 @@ function get_attachment_fields_to_edit( $post, $errors = null ) {
 			$values[] = $term->slug;
 		}
 
-		$t['value'] = join( ', ', $values );
+		$t['value'] = implode( ', ', $values );
 
 		$form_fields[ $taxonomy ] = $t;
 	}
@@ -1784,7 +1784,7 @@ function get_media_item( $attachment_id, $args = null ) {
 		}
 
 		if ( ! empty( $field['helps'] ) ) {
-			$item .= "<p class='help'>" . join( "</p>\n<p class='help'>", array_unique( (array) $field['helps'] ) ) . '</p>';
+			$item .= "<p class='help'>" . implode( "</p>\n<p class='help'>", array_unique( (array) $field['helps'] ) ) . '</p>';
 		}
 		$item .= "</td>\n\t\t</tr>\n";
 
@@ -1883,7 +1883,7 @@ function get_compat_media_markup( $attachment_id, $args = null ) {
 				$values[] = $term->slug;
 			}
 
-			$t['value']    = join( ', ', $values );
+			$t['value']    = implode( ', ', $values );
 			$t['taxonomy'] = true;
 
 			$form_fields[ $taxonomy ] = $t;
@@ -1976,7 +1976,7 @@ function get_compat_media_markup( $attachment_id, $args = null ) {
 		}
 
 		if ( ! empty( $field['helps'] ) ) {
-			$item .= "<p class='help'>" . join( "</p>\n<p class='help'>", array_unique( (array) $field['helps'] ) ) . '</p>';
+			$item .= "<p class='help'>" . implode( "</p>\n<p class='help'>", array_unique( (array) $field['helps'] ) ) . '</p>';
 		}
 
 		$item .= "</td>\n\t\t</tr>\n";
diff --git a/wp-admin/includes/misc.php b/wp-admin/includes/misc.php
index 74ac6cec27..e13a46bc91 100644
--- a/wp-admin/includes/misc.php
+++ b/wp-admin/includes/misc.php
@@ -121,7 +121,7 @@ function insert_with_markers( $filename, $marker, $insertion ) {
 		if ( $perms ) {
 			chmod( $filename, $perms | 0644 );
 		}
-	} elseif ( ! is_writeable( $filename ) ) {
+	} elseif ( ! is_writable( $filename ) ) {
 		return false;
 	}
 
diff --git a/wp-admin/includes/revision.php b/wp-admin/includes/revision.php
index 52600dce06..7718a831e4 100644
--- a/wp-admin/includes/revision.php
+++ b/wp-admin/includes/revision.php
@@ -275,7 +275,7 @@ function wp_prepare_revisions_for_js( $post, $selected_revision_id, $from = null
 	 * If we only have one revision, the initial revision is missing; This happens
 	 * when we have an autsosave and the user has clicked 'View the Autosave'
 	 */
-	if ( 1 === sizeof( $revisions ) ) {
+	if ( 1 === count( $revisions ) ) {
 		$revisions[ $post->ID ] = array(
 			'id'         => $post->ID,
 			'title'      => get_the_title( $post->ID ),
diff --git a/wp-admin/includes/taxonomy.php b/wp-admin/includes/taxonomy.php
index 7f7e60952c..de76917cd0 100644
--- a/wp-admin/includes/taxonomy.php
+++ b/wp-admin/includes/taxonomy.php
@@ -278,7 +278,7 @@ function get_terms_to_edit( $post_id, $taxonomy = 'post_tag' ) {
 		$term_names[] = $term->name;
 	}
 
-	$terms_to_edit = esc_attr( join( ',', $term_names ) );
+	$terms_to_edit = esc_attr( implode( ',', $term_names ) );
 
 	/**
 	 * Filters the comma-separated list of terms available to edit.
diff --git a/wp-admin/includes/upgrade.php b/wp-admin/includes/upgrade.php
index 0a65659492..f68ee0b9ff 100644
--- a/wp-admin/includes/upgrade.php
+++ b/wp-admin/includes/upgrade.php
@@ -1112,7 +1112,7 @@ function upgrade_130() {
 			$limit    = $option->dupes - 1;
 			$dupe_ids = $wpdb->get_col( $wpdb->prepare( "SELECT option_id FROM $wpdb->options WHERE option_name = %s LIMIT %d", $option->option_name, $limit ) );
 			if ( $dupe_ids ) {
-				$dupe_ids = join( ',', $dupe_ids );
+				$dupe_ids = implode( ',', $dupe_ids );
 				$wpdb->query( "DELETE FROM $wpdb->options WHERE option_id IN ($dupe_ids)" );
 			}
 		}
diff --git a/wp-admin/link.php b/wp-admin/link.php
index 1824f80144..5494f9f15f 100644
--- a/wp-admin/link.php
+++ b/wp-admin/link.php
@@ -60,7 +60,7 @@ switch ( $action ) {
 			wp_redirect( $this_file );
 			exit;
 		}
-		$all_links = join( ',', $linkcheck );
+		$all_links = implode( ',', $linkcheck );
 		/*
 		 * Should now have an array of links we can change:
 		 *     $q = $wpdb->query("update $wpdb->links SET link_category='$category' WHERE link_id IN ($all_links)");
diff --git a/wp-admin/menu-header.php b/wp-admin/menu-header.php
index 3e81e0bea7..1f481f8634 100644
--- a/wp-admin/menu-header.php
+++ b/wp-admin/menu-header.php
@@ -106,7 +106,7 @@ function _wp_menu_output( $menu, $submenu, $submenu_as_parent = true ) {
 			$class[] = esc_attr( $item[4] );
 		}
 
-		$class     = $class ? ' class="' . join( ' ', $class ) . '"' : '';
+		$class     = $class ? ' class="' . implode( ' ', $class ) . '"' : '';
 		$id        = ! empty( $item[5] ) ? ' id="' . preg_replace( '|[^a-zA-Z0-9_:.]|', '-', $item[5] ) . '"' : '';
 		$img       = '';
 		$img_style = '';
@@ -240,7 +240,7 @@ function _wp_menu_output( $menu, $submenu, $submenu_as_parent = true ) {
 					$class[] = esc_attr( $sub_item[4] );
 				}
 
-				$class = $class ? ' class="' . join( ' ', $class ) . '"' : '';
+				$class = $class ? ' class="' . implode( ' ', $class ) . '"' : '';
 
 				$menu_hook = get_plugin_page_hook( $sub_item[2], $item[2] );
 				$sub_file  = $sub_item[2];
diff --git a/wp-admin/network/themes.php b/wp-admin/network/themes.php
index 730ab906b1..84fbdf3106 100644
--- a/wp-admin/network/themes.php
+++ b/wp-admin/network/themes.php
@@ -89,7 +89,7 @@ if ( $action ) {
 			echo '<div class="wrap">';
 			echo '<h1>' . esc_html( $title ) . '</h1>';
 
-			$url = self_admin_url( 'update.php?action=update-selected-themes&amp;themes=' . urlencode( join( ',', $themes ) ) );
+			$url = self_admin_url( 'update.php?action=update-selected-themes&amp;themes=' . urlencode( implode( ',', $themes ) ) );
 			$url = wp_nonce_url( $url, 'bulk-update-themes' );
 
 			echo "<iframe src='$url' style='width: 100%; height:100%; min-height:850px;'></iframe>";
diff --git a/wp-admin/plugin-editor.php b/wp-admin/plugin-editor.php
index 50d5acee4f..7467ace6aa 100644
--- a/wp-admin/plugin-editor.php
+++ b/wp-admin/plugin-editor.php
@@ -195,7 +195,7 @@ $content = esc_textarea( $content );
 <h2>
 	<?php
 	if ( is_plugin_active( $plugin ) ) {
-		if ( is_writeable( $real_file ) ) {
+		if ( is_writable( $real_file ) ) {
 			/* translators: %s: Plugin file name. */
 			printf( __( 'Editing %s (active)' ), '<strong>' . esc_html( $file ) . '</strong>' );
 		} else {
@@ -203,7 +203,7 @@ $content = esc_textarea( $content );
 			printf( __( 'Browsing %s (active)' ), '<strong>' . esc_html( $file ) . '</strong>' );
 		}
 	} else {
-		if ( is_writeable( $real_file ) ) {
+		if ( is_writable( $real_file ) ) {
 			/* translators: %s: Plugin file name. */
 			printf( __( 'Editing %s (inactive)' ), '<strong>' . esc_html( $file ) . '</strong>' );
 		} else {
@@ -275,7 +275,7 @@ $content = esc_textarea( $content );
 		</div>
 	<?php endif; ?>
 
-	<?php if ( is_writeable( $real_file ) ) : ?>
+	<?php if ( is_writable( $real_file ) ) : ?>
 		<div class="editor-notices">
 		<?php if ( in_array( $plugin, (array) get_option( 'active_plugins', array() ), true ) ) { ?>
 			<div class="notice notice-warning inline active-plugin-edit-warning">
diff --git a/wp-admin/plugins.php b/wp-admin/plugins.php
index fe8ea41fb2..96d0b2cba9 100644
--- a/wp-admin/plugins.php
+++ b/wp-admin/plugins.php
@@ -162,7 +162,7 @@ if ( $action ) {
 			echo '<div class="wrap">';
 			echo '<h1>' . esc_html( $title ) . '</h1>';
 
-			$url = self_admin_url( 'update.php?action=update-selected&amp;plugins=' . urlencode( join( ',', $plugins ) ) );
+			$url = self_admin_url( 'update.php?action=update-selected&amp;plugins=' . urlencode( implode( ',', $plugins ) ) );
 			$url = wp_nonce_url( $url, 'bulk-update-plugins' );
 
 			echo "<iframe src='$url' style='width: 100%; height:100%; min-height:850px;'></iframe>";
diff --git a/wp-admin/theme-editor.php b/wp-admin/theme-editor.php
index 61e15e4bcd..3cf24cc77e 100644
--- a/wp-admin/theme-editor.php
+++ b/wp-admin/theme-editor.php
@@ -301,7 +301,7 @@ else :
 				<?php if ( is_child_theme() && $theme->get_stylesheet() === get_template() ) : ?>
 					<div class="notice notice-warning inline">
 						<p>
-							<?php if ( is_writeable( $file ) ) : ?>
+							<?php if ( is_writable( $file ) ) : ?>
 								<strong><?php _e( 'Caution:' ); ?></strong>
 							<?php endif; ?>
 							<?php _e( 'This is a file in your current parent theme.' ); ?>
@@ -309,7 +309,7 @@ else :
 					</div>
 				<?php endif; ?>
 			</div>
-			<?php if ( is_writeable( $file ) ) : ?>
+			<?php if ( is_writable( $file ) ) : ?>
 				<p class="submit">
 					<?php submit_button( __( 'Update File' ), 'primary', 'submit', false ); ?>
 					<span class="spinner"></span>
diff --git a/wp-admin/upload.php b/wp-admin/upload.php
index 3917ece191..2eb29da17d 100644
--- a/wp-admin/upload.php
+++ b/wp-admin/upload.php
@@ -162,7 +162,7 @@ if ( $doaction ) {
 			$location = add_query_arg(
 				array(
 					'trashed' => count( $post_ids ),
-					'ids'     => join( ',', $post_ids ),
+					'ids'     => implode( ',', $post_ids ),
 				),
 				$location
 			);
diff --git a/wp-content/themes/twentytwenty/inc/starter-content.php b/wp-content/themes/twentytwenty/inc/starter-content.php
index 95f7bc57aa..89be38bbe8 100644
--- a/wp-content/themes/twentytwenty/inc/starter-content.php
+++ b/wp-content/themes/twentytwenty/inc/starter-content.php
@@ -48,7 +48,7 @@ function twentytwenty_get_starter_content() {
 				'post_title'   => __( 'The New UMoMA Opens its Doors', 'twentytwenty' ),
 				// Use the above featured image with the predefined about page.
 				'thumbnail'    => '{{image-opening}}',
-				'post_content' => join(
+				'post_content' => implode(
 					'',
 					array(
 						'<!-- wp:group {"align":"wide"} -->',
diff --git a/wp-includes/bookmark-template.php b/wp-includes/bookmark-template.php
index 2db315b034..0a3840502a 100644
--- a/wp-includes/bookmark-template.php
+++ b/wp-includes/bookmark-template.php
@@ -234,7 +234,7 @@ function wp_list_bookmarks( $args = '' ) {
 		$parsed_args['class'] = explode( ' ', $parsed_args['class'] );
 	}
 	$parsed_args['class'] = array_map( 'sanitize_html_class', $parsed_args['class'] );
-	$parsed_args['class'] = trim( join( ' ', $parsed_args['class'] ) );
+	$parsed_args['class'] = trim( implode( ' ', $parsed_args['class'] ) );
 
 	if ( $parsed_args['categorize'] ) {
 		$cats = get_terms(
diff --git a/wp-includes/category-template.php b/wp-includes/category-template.php
index df4ee350a9..e2f0cb0115 100644
--- a/wp-includes/category-template.php
+++ b/wp-includes/category-template.php
@@ -1010,11 +1010,11 @@ function wp_generate_tag_cloud( $tags, $args = '' ) {
 			 * Note: this is redundant but doesn't harm.
 			 */
 			$return  = "<ul class='wp-tag-cloud' role='list'>\n\t<li>";
-			$return .= join( "</li>\n\t<li>", $a );
+			$return .= implode( "</li>\n\t<li>", $a );
 			$return .= "</li>\n</ul>\n";
 			break;
 		default:
-			$return = join( $args['separator'], $a );
+			$return = implode( $args['separator'], $a );
 			break;
 	}
 
@@ -1349,7 +1349,7 @@ function get_the_term_list( $post_id, $taxonomy, $before = '', $sep = '', $after
 	 */
 	$term_links = apply_filters( "term_links-{$taxonomy}", $links );  // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 
-	return $before . join( $sep, $term_links ) . $after;
+	return $before . implode( $sep, $term_links ) . $after;
 }
 
 /**
diff --git a/wp-includes/class-walker-nav-menu.php b/wp-includes/class-walker-nav-menu.php
index 5f4a53691c..66ba424da4 100644
--- a/wp-includes/class-walker-nav-menu.php
+++ b/wp-includes/class-walker-nav-menu.php
@@ -72,7 +72,7 @@ class Walker_Nav_Menu extends Walker {
 		 * @param stdClass $args    An object of `wp_nav_menu()` arguments.
 		 * @param int      $depth   Depth of menu item. Used for padding.
 		 */
-		$class_names = join( ' ', apply_filters( 'nav_menu_submenu_css_class', $classes, $args, $depth ) );
+		$class_names = implode( ' ', apply_filters( 'nav_menu_submenu_css_class', $classes, $args, $depth ) );
 		$class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';
 
 		$output .= "{$n}{$indent}<ul$class_names>{$n}";
@@ -150,7 +150,7 @@ class Walker_Nav_Menu extends Walker {
 		 * @param stdClass $args    An object of wp_nav_menu() arguments.
 		 * @param int      $depth   Depth of menu item. Used for padding.
 		 */
-		$class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args, $depth ) );
+		$class_names = implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args, $depth ) );
 		$class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';
 
 		/**
diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index 88a8128acd..a46b97fa5a 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -2397,7 +2397,7 @@ final class WP_Customize_Manager {
 			$notification = array();
 			foreach ( $validity->errors as $error_code => $error_messages ) {
 				$notification[ $error_code ] = array(
-					'message' => join( ' ', $error_messages ),
+					'message' => implode( ' ', $error_messages ),
 					'data'    => $validity->get_error_data( $error_code ),
 				);
 			}
diff --git a/wp-includes/class-wp-query.php b/wp-includes/class-wp-query.php
index 34d0a5de96..98f5c3c25b 100644
--- a/wp-includes/class-wp-query.php
+++ b/wp-includes/class-wp-query.php
@@ -2420,10 +2420,10 @@ class WP_Query {
 			if ( empty( $in_search_post_types ) ) {
 				$where .= ' AND 1=0 ';
 			} else {
-				$where .= " AND {$wpdb->posts}.post_type IN ('" . join( "', '", array_map( 'esc_sql', $in_search_post_types ) ) . "')";
+				$where .= " AND {$wpdb->posts}.post_type IN ('" . implode( "', '", array_map( 'esc_sql', $in_search_post_types ) ) . "')";
 			}
 		} elseif ( ! empty( $post_type ) && is_array( $post_type ) ) {
-			$where .= " AND {$wpdb->posts}.post_type IN ('" . join( "', '", esc_sql( $post_type ) ) . "')";
+			$where .= " AND {$wpdb->posts}.post_type IN ('" . implode( "', '", esc_sql( $post_type ) ) . "')";
 		} elseif ( ! empty( $post_type ) ) {
 			$where           .= $wpdb->prepare( " AND {$wpdb->posts}.post_type = %s", $post_type );
 			$post_type_object = get_post_type_object( $post_type );
@@ -2485,20 +2485,20 @@ class WP_Query {
 			}
 
 			if ( ! empty( $e_status ) ) {
-				$statuswheres[] = '(' . join( ' AND ', $e_status ) . ')';
+				$statuswheres[] = '(' . implode( ' AND ', $e_status ) . ')';
 			}
 			if ( ! empty( $r_status ) ) {
 				if ( ! empty( $q['perm'] ) && 'editable' === $q['perm'] && ! current_user_can( $edit_others_cap ) ) {
-					$statuswheres[] = "({$wpdb->posts}.post_author = $user_id " . 'AND (' . join( ' OR ', $r_status ) . '))';
+					$statuswheres[] = "({$wpdb->posts}.post_author = $user_id " . 'AND (' . implode( ' OR ', $r_status ) . '))';
 				} else {
-					$statuswheres[] = '(' . join( ' OR ', $r_status ) . ')';
+					$statuswheres[] = '(' . implode( ' OR ', $r_status ) . ')';
 				}
 			}
 			if ( ! empty( $p_status ) ) {
 				if ( ! empty( $q['perm'] ) && 'readable' === $q['perm'] && ! current_user_can( $read_private_cap ) ) {
-					$statuswheres[] = "({$wpdb->posts}.post_author = $user_id " . 'AND (' . join( ' OR ', $p_status ) . '))';
+					$statuswheres[] = "({$wpdb->posts}.post_author = $user_id " . 'AND (' . implode( ' OR ', $p_status ) . '))';
 				} else {
-					$statuswheres[] = '(' . join( ' OR ', $p_status ) . ')';
+					$statuswheres[] = '(' . implode( ' OR ', $p_status ) . ')';
 				}
 			}
 			if ( $post_status_join ) {
@@ -2669,7 +2669,7 @@ class WP_Query {
 				$post_ids[] = (int) $comment->comment_post_ID;
 			}
 
-			$post_ids = join( ',', $post_ids );
+			$post_ids = implode( ',', $post_ids );
 			$join     = '';
 			if ( $post_ids ) {
 				$where = "AND {$wpdb->posts}.ID IN ($post_ids) ";
diff --git a/wp-includes/class-wp-text-diff-renderer-table.php b/wp-includes/class-wp-text-diff-renderer-table.php
index 4bc02d3750..c55add4885 100644
--- a/wp-includes/class-wp-text-diff-renderer-table.php
+++ b/wp-includes/class-wp-text-diff-renderer-table.php
@@ -274,7 +274,7 @@ class WP_Text_Diff_Renderer_Table extends Text_Diff_Renderer {
 				// If they're too different, don't include any <ins> or <del>'s.
 				if ( preg_match_all( '!(<ins>.*?</ins>|<del>.*?</del>)!', $diff, $diff_matches ) ) {
 					// Length of all text between <ins> or <del>.
-					$stripped_matches = strlen( strip_tags( join( ' ', $diff_matches[0] ) ) );
+					$stripped_matches = strlen( strip_tags( implode( ' ', $diff_matches[0] ) ) );
 					// Since we count length of text between <ins> or <del> (instead of picking just one),
 					// we double the length of chars not in those tags.
 					$stripped_diff = strlen( strip_tags( $diff ) ) * 2 - $stripped_matches;
diff --git a/wp-includes/class-wp-user-query.php b/wp-includes/class-wp-user-query.php
index d33f6fb624..967c6b6b05 100644
--- a/wp-includes/class-wp-user-query.php
+++ b/wp-includes/class-wp-user-query.php
@@ -279,7 +279,7 @@ class WP_User_Query {
 			}
 
 			$posts_table        = $wpdb->get_blog_prefix( $blog_id ) . 'posts';
-			$this->query_where .= " AND $wpdb->users.ID IN ( SELECT DISTINCT $posts_table.post_author FROM $posts_table WHERE $posts_table.post_status = 'publish' AND $posts_table.post_type IN ( " . join( ', ', $post_types ) . ' ) )';
+			$this->query_where .= " AND $wpdb->users.ID IN ( SELECT DISTINCT $posts_table.post_author FROM $posts_table WHERE $posts_table.post_status = 'publish' AND $posts_table.post_type IN ( " . implode( ', ', $post_types ) . ' ) )';
 		}
 
 		// nicename
diff --git a/wp-includes/comment-template.php b/wp-includes/comment-template.php
index 89be475034..e3cfdef312 100644
--- a/wp-includes/comment-template.php
+++ b/wp-includes/comment-template.php
@@ -432,7 +432,7 @@ function comment_author_url_link( $linktext = '', $before = '', $after = '', $co
  */
 function comment_class( $class = '', $comment = null, $post_id = null, $echo = true ) {
 	// Separates classes with a single space, collates classes for comment DIV.
-	$class = 'class="' . join( ' ', get_comment_class( $class, $comment, $post_id ) ) . '"';
+	$class = 'class="' . implode( ' ', get_comment_class( $class, $comment, $post_id ) ) . '"';
 
 	if ( $echo ) {
 		echo $class;
diff --git a/wp-includes/comment.php b/wp-includes/comment.php
index cde13af806..71471eed12 100644
--- a/wp-includes/comment.php
+++ b/wp-includes/comment.php
@@ -3235,7 +3235,7 @@ function _prime_comment_caches( $comment_ids, $update_meta_cache = true ) {
 
 	$non_cached_ids = _get_non_cached_ids( $comment_ids, 'comment' );
 	if ( ! empty( $non_cached_ids ) ) {
-		$fresh_comments = $wpdb->get_results( sprintf( "SELECT $wpdb->comments.* FROM $wpdb->comments WHERE comment_ID IN (%s)", join( ',', array_map( 'intval', $non_cached_ids ) ) ) );
+		$fresh_comments = $wpdb->get_results( sprintf( "SELECT $wpdb->comments.* FROM $wpdb->comments WHERE comment_ID IN (%s)", implode( ',', array_map( 'intval', $non_cached_ids ) ) ) );
 
 		update_comment_cache( $fresh_comments, $update_meta_cache );
 	}
diff --git a/wp-includes/compat.php b/wp-includes/compat.php
index e322dd26de..7f6c59f03c 100644
--- a/wp-includes/compat.php
+++ b/wp-includes/compat.php
@@ -127,7 +127,7 @@ function _mb_substr( $str, $start, $length = null, $encoding = null ) {
 		// If there's anything left over, repeat the loop.
 	} while ( count( $pieces ) > 1 && $str = array_pop( $pieces ) );
 
-	return join( '', array_slice( $chars, $start, $length ) );
+	return implode( '', array_slice( $chars, $start, $length ) );
 }
 
 if ( ! function_exists( 'mb_strlen' ) ) :
diff --git a/wp-includes/embed.php b/wp-includes/embed.php
index 8dbd7b6927..80c9ba0980 100644
--- a/wp-includes/embed.php
+++ b/wp-includes/embed.php
@@ -204,7 +204,7 @@ function wp_maybe_load_embeds() {
 	 *
 	 * @param callable $handler Audio embed handler callback function.
 	 */
-	wp_embed_register_handler( 'audio', '#^https?://.+?\.(' . join( '|', wp_get_audio_extensions() ) . ')$#i', apply_filters( 'wp_audio_embed_handler', 'wp_embed_handler_audio' ), 9999 );
+	wp_embed_register_handler( 'audio', '#^https?://.+?\.(' . implode( '|', wp_get_audio_extensions() ) . ')$#i', apply_filters( 'wp_audio_embed_handler', 'wp_embed_handler_audio' ), 9999 );
 
 	/**
 	 * Filters the video embed handler callback.
@@ -213,7 +213,7 @@ function wp_maybe_load_embeds() {
 	 *
 	 * @param callable $handler Video embed handler callback function.
 	 */
-	wp_embed_register_handler( 'video', '#^https?://.+?\.(' . join( '|', wp_get_video_extensions() ) . ')$#i', apply_filters( 'wp_video_embed_handler', 'wp_embed_handler_video' ), 9999 );
+	wp_embed_register_handler( 'video', '#^https?://.+?\.(' . implode( '|', wp_get_video_extensions() ) . ')$#i', apply_filters( 'wp_video_embed_handler', 'wp_embed_handler_video' ), 9999 );
 }
 
 /**
@@ -842,7 +842,7 @@ function wp_filter_oembed_iframe_title_attribute( $result, $data, $url ) {
 
 	if ( isset( $attrs['title'] ) ) {
 		unset( $attrs['title'] );
-		$attr_string = join( ' ', wp_list_pluck( $attrs, 'whole' ) );
+		$attr_string = implode( ' ', wp_list_pluck( $attrs, 'whole' ) );
 		$result      = str_replace( $matches[0], '<iframe ' . trim( $attr_string ) . '>', $result );
 	}
 	return str_ireplace( '<iframe ', sprintf( '<iframe title="%s" ', esc_attr( $title ) ), $result );
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 1187efc52d..a0c2eda313 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -722,7 +722,7 @@ function _get_wptexturize_split_regex( $shortcode_regex = '' ) {
  * @return string The regular expression
  */
 function _get_wptexturize_shortcode_regex( $tagnames ) {
-	$tagregexp = join( '|', array_map( 'preg_quote', $tagnames ) );
+	$tagregexp = implode( '|', array_map( 'preg_quote', $tagnames ) );
 	$tagregexp = "(?:$tagregexp)(?=[\\s\\]\\/])"; // Excerpt of get_shortcode_regex().
 	// phpcs:disable Squiz.Strings.ConcatenationSpacing.PaddingFound -- don't remove regex indentation
 	$regex =
@@ -824,7 +824,7 @@ function shortcode_unautop( $pee ) {
 		return $pee;
 	}
 
-	$tagregexp = join( '|', array_map( 'preg_quote', array_keys( $shortcode_tags ) ) );
+	$tagregexp = implode( '|', array_map( 'preg_quote', array_keys( $shortcode_tags ) ) );
 	$spaces    = wp_spaces_regexp();
 
 	// phpcs:disable Squiz.Strings.ConcatenationSpacing.PaddingFound,WordPress.WhiteSpace.PrecisionAlignment.Found -- don't remove regex indentation
@@ -3232,7 +3232,7 @@ function wp_targeted_link_rel_callback( $matches ) {
 	}
 
 	$atts['rel']['whole'] = 'rel="' . esc_attr( $rel ) . '"';
-	$link_html            = join( ' ', array_column( $atts, 'whole' ) );
+	$link_html            = implode( ' ', array_column( $atts, 'whole' ) );
 
 	if ( $is_escaped ) {
 		$link_html = preg_replace( '/[\'"]/', '\\\\$0', $link_html );
@@ -3696,7 +3696,7 @@ function sanitize_email( $email ) {
 	}
 
 	// Join valid subs into the new domain.
-	$domain = join( '.', $new_subs );
+	$domain = implode( '.', $new_subs );
 
 	// Put the email back together.
 	$sanitized_email = $local . '@' . $domain;
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index e3f9896211..0d034a5b08 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -467,7 +467,7 @@ function size_format( $bytes, $decimals = 0 ) {
 	}
 
 	foreach ( $quant as $unit => $mag ) {
-		if ( doubleval( $bytes ) >= $mag ) {
+		if ( (float) $bytes >= $mag ) {
 			return number_format_i18n( $bytes / $mag, $decimals ) . ' ' . $unit;
 		}
 	}
@@ -3431,7 +3431,7 @@ function _default_wp_die_handler( $message, $title = '', $args = array() ) {
 				array( $message ),
 				wp_list_pluck( $parsed_args['additional_errors'], 'message' )
 			);
-			$message = "<ul>\n\t\t<li>" . join( "</li>\n\t\t<li>", $message ) . "</li>\n\t</ul>";
+			$message = "<ul>\n\t\t<li>" . implode( "</li>\n\t\t<li>", $message ) . "</li>\n\t</ul>";
 		}
 
 		$message = sprintf(
@@ -5880,7 +5880,7 @@ function wp_timezone_choice( $selected_zone, $locale = null ) {
 		}
 
 		// Build the value.
-		$value    = join( '/', $value );
+		$value    = implode( '/', $value );
 		$selected = '';
 		if ( $value === $selected_zone ) {
 			$selected = 'selected="selected" ';
@@ -5981,7 +5981,7 @@ function wp_timezone_choice( $selected_zone, $locale = null ) {
 	}
 	$structure[] = '</optgroup>';
 
-	return join( "\n", $structure );
+	return implode( "\n", $structure );
 }
 
 /**
@@ -6419,7 +6419,7 @@ function wp_debug_backtrace_summary( $ignore_class = null, $skip_frames = 0, $pr
 		}
 	}
 	if ( $pretty ) {
-		return join( ', ', array_reverse( $caller ) );
+		return implode( ', ', array_reverse( $caller ) );
 	} else {
 		return $caller;
 	}
diff --git a/wp-includes/general-template.php b/wp-includes/general-template.php
index dc5b374121..15c4974304 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -4345,12 +4345,12 @@ function paginate_links( $args = '' ) {
 
 		case 'list':
 			$r .= "<ul class='page-numbers'>\n\t<li>";
-			$r .= join( "</li>\n\t<li>", $page_links );
+			$r .= implode( "</li>\n\t<li>", $page_links );
 			$r .= "</li>\n</ul>\n";
 			break;
 
 		default:
-			$r = join( "\n", $page_links );
+			$r = implode( "\n", $page_links );
 			break;
 	}
 
diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index 226cc2d8fd..0c6b75ea24 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -1617,7 +1617,7 @@ function wp_dropdown_languages( $args = array() ) {
 
 	// Combine the output string.
 	$output  = sprintf( '<select name="%s" id="%s">', esc_attr( $parsed_args['name'] ), esc_attr( $parsed_args['id'] ) );
-	$output .= join( "\n", $structure );
+	$output .= implode( "\n", $structure );
 	$output .= '</select>';
 
 	if ( $parsed_args['echo'] ) {
diff --git a/wp-includes/media.php b/wp-includes/media.php
index ab33c88c04..383ad9930f 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -1035,7 +1035,7 @@ function wp_get_attachment_image( $attachment_id, $size = 'thumbnail', $icon = f
 		$size_class = $size;
 
 		if ( is_array( $size_class ) ) {
-			$size_class = join( 'x', $size_class );
+			$size_class = implode( 'x', $size_class );
 		}
 
 		$default_attr = array(
@@ -2950,7 +2950,7 @@ function wp_audio_shortcode( $attr, $content = '' ) {
 		$html .= "<!--[if lt IE 9]><script>document.createElement('audio');</script><![endif]-->\n";
 	}
 
-	$html .= sprintf( '<audio %s controls="controls">', join( ' ', $attr_strings ) );
+	$html .= sprintf( '<audio %s controls="controls">', implode( ' ', $attr_strings ) );
 
 	$fileurl = '';
 	$source  = '<source type="%s" src="%s" />';
@@ -3218,7 +3218,7 @@ function wp_video_shortcode( $attr, $content = '' ) {
 		$html .= "<!--[if lt IE 9]><script>document.createElement('video');</script><![endif]-->\n";
 	}
 
-	$html .= sprintf( '<video %s controls="controls">', join( ' ', $attr_strings ) );
+	$html .= sprintf( '<video %s controls="controls">', implode( ' ', $attr_strings ) );
 
 	$fileurl = '';
 	$source  = '<source type="%s" src="%s" />';
diff --git a/wp-includes/meta.php b/wp-includes/meta.php
index 3cef8c1363..e1c1f92e48 100644
--- a/wp-includes/meta.php
+++ b/wp-includes/meta.php
@@ -1055,7 +1055,7 @@ function update_meta_cache( $meta_type, $object_ids ) {
 	}
 
 	// Get meta info.
-	$id_list   = join( ',', $non_cached_ids );
+	$id_list   = implode( ',', $non_cached_ids );
 	$id_column = ( 'user' === $meta_type ) ? 'umeta_id' : 'meta_id';
 
 	$meta_list = $wpdb->get_results( "SELECT $column, meta_key, meta_value FROM $table WHERE $column IN ($id_list) ORDER BY $id_column ASC", ARRAY_A );
diff --git a/wp-includes/ms-network.php b/wp-includes/ms-network.php
index 0434fa8acb..91001ab9a0 100644
--- a/wp-includes/ms-network.php
+++ b/wp-includes/ms-network.php
@@ -131,7 +131,7 @@ function _prime_network_caches( $network_ids ) {
 
 	$non_cached_ids = _get_non_cached_ids( $network_ids, 'networks' );
 	if ( ! empty( $non_cached_ids ) ) {
-		$fresh_networks = $wpdb->get_results( sprintf( "SELECT $wpdb->site.* FROM $wpdb->site WHERE id IN (%s)", join( ',', array_map( 'intval', $non_cached_ids ) ) ) ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
+		$fresh_networks = $wpdb->get_results( sprintf( "SELECT $wpdb->site.* FROM $wpdb->site WHERE id IN (%s)", implode( ',', array_map( 'intval', $non_cached_ids ) ) ) ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
 
 		update_network_cache( $fresh_networks );
 	}
diff --git a/wp-includes/ms-site.php b/wp-includes/ms-site.php
index b90dde3cd0..31d1c7ce99 100644
--- a/wp-includes/ms-site.php
+++ b/wp-includes/ms-site.php
@@ -352,7 +352,7 @@ function _prime_site_caches( $ids, $update_meta_cache = true ) {
 
 	$non_cached_ids = _get_non_cached_ids( $ids, 'sites' );
 	if ( ! empty( $non_cached_ids ) ) {
-		$fresh_sites = $wpdb->get_results( sprintf( "SELECT * FROM $wpdb->blogs WHERE blog_id IN (%s)", join( ',', array_map( 'intval', $non_cached_ids ) ) ) ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
+		$fresh_sites = $wpdb->get_results( sprintf( "SELECT * FROM $wpdb->blogs WHERE blog_id IN (%s)", implode( ',', array_map( 'intval', $non_cached_ids ) ) ) ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
 
 		update_site_cache( $fresh_sites, $update_meta_cache );
 	}
diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index a822ff3bea..68187fcf05 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -2723,7 +2723,7 @@ if ( ! function_exists( 'get_avatar' ) ) :
 			esc_attr( $args['alt'] ),
 			esc_url( $url ),
 			esc_url( $url2x ) . ' 2x',
-			esc_attr( join( ' ', $class ) ),
+			esc_attr( implode( ' ', $class ) ),
 			(int) $args['height'],
 			(int) $args['width'],
 			$extra_attr
diff --git a/wp-includes/post-template.php b/wp-includes/post-template.php
index c65b2e473b..0aff64d119 100644
--- a/wp-includes/post-template.php
+++ b/wp-includes/post-template.php
@@ -456,7 +456,7 @@ function has_excerpt( $post = 0 ) {
  */
 function post_class( $class = '', $post_id = null ) {
 	// Separates classes with a single space, collates classes for post DIV.
-	echo 'class="' . esc_attr( join( ' ', get_post_class( $class, $post_id ) ) ) . '"';
+	echo 'class="' . esc_attr( implode( ' ', get_post_class( $class, $post_id ) ) ) . '"';
 }
 
 /**
@@ -592,7 +592,7 @@ function get_post_class( $class = '', $post_id = null ) {
  */
 function body_class( $class = '' ) {
 	// Separates class names with a single space, collates class names for body element.
-	echo 'class="' . esc_attr( join( ' ', get_body_class( $class ) ) ) . '"';
+	echo 'class="' . esc_attr( implode( ' ', get_body_class( $class ) ) ) . '"';
 }
 
 /**
diff --git a/wp-includes/post.php b/wp-includes/post.php
index 32bfb1cac8..6e968f3f9f 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -2955,7 +2955,7 @@ function wp_post_mime_type_where( $post_mime_types, $table_alias = '' ) {
 	}
 
 	if ( ! empty( $wheres ) ) {
-		$where = ' AND (' . join( ' OR ', $wheres ) . ') ';
+		$where = ' AND (' . implode( ' OR ', $wheres ) . ') ';
 	}
 
 	return $where;
@@ -7466,7 +7466,7 @@ function _prime_post_caches( $ids, $update_term_cache = true, $update_meta_cache
 
 	$non_cached_ids = _get_non_cached_ids( $ids, 'posts' );
 	if ( ! empty( $non_cached_ids ) ) {
-		$fresh_posts = $wpdb->get_results( sprintf( "SELECT $wpdb->posts.* FROM $wpdb->posts WHERE ID IN (%s)", join( ',', $non_cached_ids ) ) );
+		$fresh_posts = $wpdb->get_results( sprintf( "SELECT $wpdb->posts.* FROM $wpdb->posts WHERE ID IN (%s)", implode( ',', $non_cached_ids ) ) );
 
 		update_post_caches( $fresh_posts, 'any', $update_term_cache, $update_meta_cache );
 	}
diff --git a/wp-includes/shortcodes.php b/wp-includes/shortcodes.php
index d821caee9e..90ca735dae 100644
--- a/wp-includes/shortcodes.php
+++ b/wp-includes/shortcodes.php
@@ -252,7 +252,7 @@ function get_shortcode_regex( $tagnames = null ) {
 	if ( empty( $tagnames ) ) {
 		$tagnames = array_keys( $shortcode_tags );
 	}
-	$tagregexp = join( '|', array_map( 'preg_quote', $tagnames ) );
+	$tagregexp = implode( '|', array_map( 'preg_quote', $tagnames ) );
 
 	// WARNING! Do not change this regex without changing do_shortcode_tag() and strip_shortcode_tag().
 	// Also, see shortcode_unautop() and shortcode.js.
diff --git a/wp-includes/taxonomy.php b/wp-includes/taxonomy.php
index e891af68d8..06fa0a0f47 100644
--- a/wp-includes/taxonomy.php
+++ b/wp-includes/taxonomy.php
@@ -2708,7 +2708,7 @@ function wp_set_object_terms( $object_id, $terms, $taxonomy, $append = false ) {
 		}
 
 		if ( $values ) {
-			if ( false === $wpdb->query( "INSERT INTO $wpdb->term_relationships (object_id, term_taxonomy_id, term_order) VALUES " . join( ',', $values ) . ' ON DUPLICATE KEY UPDATE term_order = VALUES(term_order)' ) ) {
+			if ( false === $wpdb->query( "INSERT INTO $wpdb->term_relationships (object_id, term_taxonomy_id, term_order) VALUES " . implode( ',', $values ) . ' ON DUPLICATE KEY UPDATE term_order = VALUES(term_order)' ) ) {
 				return new WP_Error( 'db_insert_error', __( 'Could not insert term relationship into the database.' ), $wpdb->last_error );
 			}
 		}
@@ -4058,7 +4058,7 @@ function _prime_term_caches( $term_ids, $update_meta_cache = true ) {
 
 	$non_cached_ids = _get_non_cached_ids( $term_ids, 'terms' );
 	if ( ! empty( $non_cached_ids ) ) {
-		$fresh_terms = $wpdb->get_results( sprintf( "SELECT t.*, tt.* FROM $wpdb->terms AS t INNER JOIN $wpdb->term_taxonomy AS tt ON t.term_id = tt.term_id WHERE t.term_id IN (%s)", join( ',', array_map( 'intval', $non_cached_ids ) ) ) );
+		$fresh_terms = $wpdb->get_results( sprintf( "SELECT t.*, tt.* FROM $wpdb->terms AS t INNER JOIN $wpdb->term_taxonomy AS tt ON t.term_id = tt.term_id WHERE t.term_id IN (%s)", implode( ',', array_map( 'intval', $non_cached_ids ) ) ) );
 
 		update_term_cache( $fresh_terms, $update_meta_cache );
 
@@ -4708,7 +4708,7 @@ function the_taxonomies( $args = array() ) {
 
 	$parsed_args = wp_parse_args( $args, $defaults );
 
-	echo $parsed_args['before'] . join( $parsed_args['sep'], get_the_taxonomies( $parsed_args['post'], $parsed_args ) ) . $parsed_args['after'];
+	echo $parsed_args['before'] . implode( $parsed_args['sep'], get_the_taxonomies( $parsed_args['post'], $parsed_args ) ) . $parsed_args['after'];
 }
 
 /**
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 5fa7a23146..a6ecad3ffe 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -2149,7 +2149,7 @@ function get_theme_starter_content() {
 				'text',
 				array(
 					'title'  => _x( 'Find Us', 'Theme starter content' ),
-					'text'   => join(
+					'text'   => implode(
 						'',
 						array(
 							'<strong>' . _x( 'Address', 'Theme starter content' ) . "</strong>\n",
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 725a605e1f..87b0bddb7f 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-49192';
+$wp_version = '5.6-alpha-49193';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/widgets/class-wp-widget-custom-html.php b/wp-includes/widgets/class-wp-widget-custom-html.php
index a3314280b3..8412a4d371 100644
--- a/wp-includes/widgets/class-wp-widget-custom-html.php
+++ b/wp-includes/widgets/class-wp-widget-custom-html.php
@@ -281,7 +281,7 @@ class WP_Widget_Custom_HTML extends WP_Widget {
 					<# if ( data.codeEditorDisabled ) { #>
 						<p>
 							<?php _e( 'Some HTML tags are not permitted, including:' ); ?>
-							<code><?php echo join( '</code>, <code>', $disallowed_html ); ?></code>
+							<code><?php echo implode( '</code>, <code>', $disallowed_html ); ?></code>
 						</p>
 					<# } #>
 				<?php endif; ?>
diff --git a/wp-includes/widgets/class-wp-widget-media-image.php b/wp-includes/widgets/class-wp-widget-media-image.php
index 01b7bae394..5ce3c9019a 100644
--- a/wp-includes/widgets/class-wp-widget-media-image.php
+++ b/wp-includes/widgets/class-wp-widget-media-image.php
@@ -219,7 +219,7 @@ class WP_Widget_Media_Image extends WP_Widget_Media {
 				$width        = empty( $caption_size[0] ) ? 0 : $caption_size[0];
 			}
 
-			$image_attributes['class'] .= sprintf( ' attachment-%1$s size-%1$s', is_array( $size ) ? join( 'x', $size ) : $size );
+			$image_attributes['class'] .= sprintf( ' attachment-%1$s size-%1$s', is_array( $size ) ? implode( 'x', $size ) : $size );
 
 			$image = wp_get_attachment_image( $attachment->ID, $size, false, $image_attributes );
 
diff --git a/wp-includes/widgets/class-wp-widget-media.php b/wp-includes/widgets/class-wp-widget-media.php
index 9c0dc05275..59aeeeacdb 100644
--- a/wp-includes/widgets/class-wp-widget-media.php
+++ b/wp-includes/widgets/class-wp-widget-media.php
@@ -208,7 +208,7 @@ abstract class WP_Widget_Media extends WP_Widget {
 		}
 		$tokens = array_map( 'sanitize_html_class', $tokens );
 		$tokens = array_filter( $tokens );
-		return join( ' ', $tokens );
+		return implode( ' ', $tokens );
 	}
 
 	/**
@@ -343,7 +343,7 @@ abstract class WP_Widget_Media extends WP_Widget {
 				class="media-widget-instance-property"
 				name="<?php echo esc_attr( $this->get_field_name( $name ) ); ?>"
 				id="<?php echo esc_attr( $this->get_field_id( $name ) ); // Needed specifically by wpWidgets.appendTitle(). ?>"
-				value="<?php echo esc_attr( is_array( $value ) ? join( ',', $value ) : (string) $value ); ?>"
+				value="<?php echo esc_attr( is_array( $value ) ? implode( ',', $value ) : (string) $value ); ?>"
 			/>
 			<?php
 		endforeach;