function import_theme_starter_content( $starter_content = array() ) {
		if ( empty( $starter_content ) ) {
			$starter_content = get_theme_starter_content();
		}

		$changeset_data = array();
		if ( $this->changeset_post_id() ) {
			/*
			 * Don't re-import starter content into a changeset saved persistently.
			 * This will need to be revisited in the future once theme switching
			 * is allowed with drafted/scheduled changesets, since switching to
			 * another theme could result in more starter content being applied.
			 * However, when doing an explicit save it is currently possible for
			 * nav menus and nav menu items specifically to lose their starter_content
			 * flags, thus resulting in duplicates being created since they fail
			 * to get re-used. See #40146.
			 */
			if ( 'auto-draft' !== get_post_status( $this->changeset_post_id() ) ) {
				return;
			}

			$changeset_data = $this->get_changeset_post_data( $this->changeset_post_id() );
		}

		$sidebars_widgets = isset( $starter_content['widgets'] ) && ! empty( $this->widgets ) ? $starter_content['widgets'] : array();
		$attachments      = isset( $starter_content['attachments'] ) && ! empty( $this->nav_menus ) ? $starter_content['attachments'] : array();
		$posts            = isset( $starter_content['posts'] ) && ! empty( $this->nav_menus ) ? $starter_content['posts'] : array();
		$options          = isset( $starter_content['options'] ) ? $starter_content['options'] : array();
		$nav_menus        = isset( $starter_content['nav_menus'] ) && ! empty( $this->nav_menus ) ? $starter_content['nav_menus'] : array();
		$theme_mods       = isset( $starter_content['theme_mods'] ) ? $starter_content['theme_mods'] : array();

		// Widgets.
		$max_widget_numbers = array();
		foreach ( $sidebars_widgets as $sidebar_id => $widgets ) {
			$sidebar_widget_ids = array();
			foreach ( $widgets as $widget ) {
				list( $id_base, $instance ) = $widget;

				if ( ! isset( $max_widget_numbers[ $id_base ] ) ) {

					// When $settings is an array-like object, get an intrinsic array for use with array_keys().
					$settings = get_option( "widget_{$id_base}", array() );
					if ( $settings instanceof ArrayObject || $settings instanceof ArrayIterator ) {
						$settings = $settings->getArrayCopy();
					}

					// Find the max widget number for this type.
					$widget_numbers = array_keys( $settings );
					if ( count( $widget_numbers ) > 0 ) {
						$widget_numbers[]               = 1;
						$max_widget_numbers[ $id_base ] = max( ...$widget_numbers );
					} else {
						$max_widget_numbers[ $id_base ] = 1;
					}
				}
				$max_widget_numbers[ $id_base ] += 1;

				$widget_id  = sprintf( '%s-%d', $id_base, $max_widget_numbers[ $id_base ] );
				$setting_id = sprintf( 'widget_%s[%d]', $id_base, $max_widget_numbers[ $id_base ] );

				$setting_value = $this->widgets->sanitize_widget_js_instance( $instance );
				if ( empty( $changeset_data[ $setting_id ] ) || ! empty( $changeset_data[ $setting_id ]['starter_content'] ) ) {
					$this->set_post_value( $setting_id, $setting_value );
					$this->pending_starter_content_settings_ids[] = $setting_id;
				}
				$sidebar_widget_ids[] = $widget_id;
			}

			$setting_id = sprintf( 'sidebars_widgets[%s]', $sidebar_id );
			if ( empty( $changeset_data[ $setting_id ] ) || ! empty( $changeset_data[ $setting_id ]['starter_content'] ) ) {
				$this->set_post_value( $setting_id, $sidebar_widget_ids );
				$this->pending_starter_content_settings_ids[] = $setting_id;
			}
		}

		$starter_content_auto_draft_post_ids = array();
		if ( ! empty( $changeset_data['nav_menus_created_posts']['value'] ) ) {
			$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, $changeset_data['nav_menus_created_posts']['value'] );
		}

		// Make an index of all the posts needed and what their slugs are.
		$needed_posts = array();
		$attachments  = $this->prepare_starter_content_attachments( $attachments );
		foreach ( $attachments as $attachment ) {
			$key                  = 'attachment:' . $attachment['post_name'];
			$needed_posts[ $key ] = true;
		}
		foreach ( array_keys( $posts ) as $post_symbol ) {
			if ( empty( $posts[ $post_symbol ]['post_name'] ) && empty( $posts[ $post_symbol ]['post_title'] ) ) {
				unset( $posts[ $post_symbol ] );
				continue;
			}
			if ( empty( $posts[ $post_symbol ]['post_name'] ) ) {
				$posts[ $post_symbol ]['post_name'] = sanitize_title( $posts[ $post_symbol ]['post_title'] );
			}
			if ( empty( $posts[ $post_symbol ]['post_type'] ) ) {
				$posts[ $post_symbol ]['post_type'] = 'post';
			}
			$needed_posts[ $posts[ $post_symbol ]['post_type'] . ':' . $posts[ $post_symbol ]['post_name'] ] = true;
		}
		$all_post_slugs = array_merge(
			wp_list_pluck( $attachments, 'post_name' ),
			wp_list_pluck( $posts, 'post_name' )
		);

		/*
		 * Obtain all post types referenced in starter content to use in query.
		 * This is needed because 'any' will not account for post types not yet registered.
		 */
		$post_types = array_filter( array_merge( array( 'attachment' ), wp_list_pluck( $posts, 'post_type' ) ) );

		// Re-use auto-draft starter content posts referenced in the current customized state.
		$existing_starter_content_posts = array();
		if ( ! empty( $starter_content_auto_draft_post_ids ) ) {
			$existing_posts_query = new WP_Query(
				array(
					'post__in'       => $starter_content_auto_draft_post_ids,
					'post_status'    => 'auto-draft',
					'post_type'      => $post_types,
					'posts_per_page' => -1,
				)
			);
			foreach ( $existing_posts_query->posts as $existing_post ) {
				$post_name = $existing_post->post_name;
				if ( empty( $post_name ) ) {
					$post_name = get_post_meta( $existing_post->ID, '_customize_draft_post_name', true );
				}
				$existing_starter_content_posts[ $existing_post->post_type . ':' . $post_name ] = $existing_post;
			}
		}

		// Re-use non-auto-draft posts.
		if ( ! empty( $all_post_slugs ) ) {
			$existing_posts_query = new WP_Query(
				array(
					'post_name__in'  => $all_post_slugs,
					'post_status'    => array_diff( get_post_stati(), array( 'auto-draft' ) ),
					'post_type'      => 'any',
					'posts_per_page' => -1,
				)
			);
			foreach ( $existing_posts_query->posts as $existing_post ) {
				$key = $existing_post->post_type . ':' . $existing_post->post_name;
				if ( isset( $needed_posts[ $key ] ) && ! isset( $existing_starter_content_posts[ $key ] ) ) {
					$existing_starter_content_posts[ $key ] = $existing_post;
				}
			}
		}

		// Attachments are technically posts but handled differently.
		if ( ! empty( $attachments ) ) {

			$attachment_ids = array();

			foreach ( $attachments as $symbol => $attachment ) {
				$file_array    = array(
					'name' => $attachment['file_name'],
				);
				$file_path     = $attachment['file_path'];
				$attachment_id = null;
				$attached_file = null;
				if ( isset( $existing_starter_content_posts[ 'attachment:' . $attachment['post_name'] ] ) ) {
					$attachment_post = $existing_starter_content_posts[ 'attachment:' . $attachment['post_name'] ];
					$attachment_id   = $attachment_post->ID;
					$attached_file   = get_attached_file( $attachment_id );
					if ( empty( $attached_file ) || ! file_exists( $attached_file ) ) {
						$attachment_id = null;
						$attached_file = null;
					} elseif ( $this->get_stylesheet() !== get_post_meta( $attachment_post->ID, '_starter_content_theme', true ) ) {

						// Re-generate attachment metadata since it was previously generated for a different theme.
						$metadata = wp_generate_attachment_metadata( $attachment_post->ID, $attached_file );
						wp_update_attachment_metadata( $attachment_id, $metadata );
						update_post_meta( $attachment_id, '_starter_content_theme', $this->get_stylesheet() );
					}
				}

				// Insert the attachment auto-draft because it doesn't yet exist or the attached file is gone.
				if ( ! $attachment_id ) {

					// Copy file to temp location so that original file won't get deleted from theme after sideloading.
					$temp_file_name = wp_tempnam( wp_basename( $file_path ) );
					if ( $temp_file_name && copy( $file_path, $temp_file_name ) ) {
						$file_array['tmp_name'] = $temp_file_name;
					}
					if ( empty( $file_array['tmp_name'] ) ) {
						continue;
					}

					$attachment_post_data = array_merge(
						wp_array_slice_assoc( $attachment, array( 'post_title', 'post_content', 'post_excerpt' ) ),
						array(
							'post_status' => 'auto-draft', // So attachment will be garbage collected in a week if changeset is never published.
						)
					);

					$attachment_id = media_handle_sideload( $file_array, 0, null, $attachment_post_data );
					if ( is_wp_error( $attachment_id ) ) {
						continue;
					}
					update_post_meta( $attachment_id, '_starter_content_theme', $this->get_stylesheet() );
					update_post_meta( $attachment_id, '_customize_draft_post_name', $attachment['post_name'] );
				}

				$attachment_ids[ $symbol ] = $attachment_id;
			}
			$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, array_values( $attachment_ids ) );
		}

		// Posts & pages.
		if ( ! empty( $posts ) ) {
			foreach ( array_keys( $posts ) as $post_symbol ) {
				if ( empty( $posts[ $post_symbol ]['post_type'] ) || empty( $posts[ $post_symbol ]['post_name'] ) ) {
					continue;
				}
				$post_type = $posts[ $post_symbol ]['post_type'];
				if ( ! empty( $posts[ $post_symbol ]['post_name'] ) ) {
					$post_name = $posts[ $post_symbol ]['post_name'];
				} elseif ( ! empty( $posts[ $post_symbol ]['post_title'] ) ) {
					$post_name = sanitize_title( $posts[ $post_symbol ]['post_title'] );
				} else {
					continue;
				}

				// Use existing auto-draft post if one already exists with the same type and name.
				if ( isset( $existing_starter_content_posts[ $post_type . ':' . $post_name ] ) ) {
					$posts[ $post_symbol ]['ID'] = $existing_starter_content_posts[ $post_type . ':' . $post_name ]->ID;
					continue;
				}

				// Translate the featured image symbol.
				if ( ! empty( $posts[ $post_symbol ]['thumbnail'] )
					&& preg_match( '/^{{(?P<symbol>.+)}}$/', $posts[ $post_symbol ]['thumbnail'], $matches )
					&& isset( $attachment_ids[ $matches['symbol'] ] ) ) {
					$posts[ $post_symbol ]['meta_input']['_thumbnail_id'] = $attachment_ids[ $matches['symbol'] ];
				}

				if ( ! empty( $posts[ $post_symbol ]['template'] ) ) {
					$posts[ $post_symbol ]['meta_input']['_wp_page_template'] = $posts[ $post_symbol ]['template'];
				}

				$r = $this->nav_menus->insert_auto_draft_post( $posts[ $post_symbol ] );
				if ( $r instanceof WP_Post ) {
					$posts[ $post_symbol ]['ID'] = $r->ID;
				}
			}

			$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, wp_list_pluck( $posts, 'ID' ) );
		}

		// The nav_menus_created_posts setting is why nav_menus component is dependency for adding posts.
		if ( ! empty( $this->nav_menus ) && ! empty( $starter_content_auto_draft_post_ids ) ) {
			$setting_id = 'nav_menus_created_posts';
			$this->set_post_value( $setting_id, array_unique( array_values( $starter_content_auto_draft_post_ids ) ) );
			$this->pending_starter_content_settings_ids[] = $setting_id;
		}

		// Nav menus.
		$placeholder_id              = -1;
		$reused_nav_menu_setting_ids = array();
		foreach ( $nav_menus as $nav_menu_location => $nav_menu ) {

			$nav_menu_term_id    = null;
			$nav_menu_setting_id = null;
			$matches             = array();

			// Look for an existing placeholder menu with starter content to re-use.
			foreach ( $changeset_data as $setting_id => $setting_params ) {
				$can_reuse = (
					! empty( $setting_params['starter_content'] )
					&&
					! in_array( $setting_id, $reused_nav_menu_setting_ids, true )
					&&
					preg_match( '#^nav_menu\[(?P<nav_menu_id>-?\d+)\]$#', $setting_id, $matches )
				);
				if ( $can_reuse ) {
					$nav_menu_term_id              = intval( $matches['nav_menu_id'] );
					$nav_menu_setting_id           = $setting_id;
					$reused_nav_menu_setting_ids[] = $setting_id;
					break;
				}
			}

			if ( ! $nav_menu_term_id ) {
				while ( isset( $changeset_data[ sprintf( 'nav_menu[%d]', $placeholder_id ) ] ) ) {
					$placeholder_id--;
				}
				$nav_menu_term_id    = $placeholder_id;
				$nav_menu_setting_id = sprintf( 'nav_menu[%d]', $placeholder_id );
			}

			$this->set_post_value(
				$nav_menu_setting_id,
				array(
					'name' => isset( $nav_menu['name'] ) ? $nav_menu['name'] : $nav_menu_location,
				)
			);
			$this->pending_starter_content_settings_ids[] = $nav_menu_setting_id;

			// @todo Add support for menu_item_parent.
			$position = 0;
			foreach ( $nav_menu['items'] as $nav_menu_item ) {
				$nav_menu_item_setting_id = sprintf( 'nav_menu_item[%d]', $placeholder_id-- );
				if ( ! isset( $nav_menu_item['position'] ) ) {
					$nav_menu_item['position'] = $position++;
				}
				$nav_menu_item['nav_menu_term_id'] = $nav_menu_term_id;

				if ( isset( $nav_menu_item['object_id'] ) ) {
					if ( 'post_type' === $nav_menu_item['type'] && preg_match( '/^{{(?P<symbol>.+)}}$/', $nav_menu_item['object_id'], $matches ) && isset( $posts[ $matches['symbol'] ] ) ) {
						$nav_menu_item['object_id'] = $posts[ $matches['symbol'] ]['ID'];
						if ( empty( $nav_menu_item['title'] ) ) {
							$original_object        = get_post( $nav_menu_item['object_id'] );
							$nav_menu_item['title'] = $original_object->post_title;
						}
					} else {
						continue;
					}
				} else {
					$nav_menu_item['object_id'] = 0;
				}

				if ( empty( $changeset_data[ $nav_menu_item_setting_id ] ) || ! empty( $changeset_data[ $nav_menu_item_setting_id ]['starter_content'] ) ) {
					$this->set_post_value( $nav_menu_item_setting_id, $nav_menu_item );
					$this->pending_starter_content_settings_ids[] = $nav_menu_item_setting_id;
				}
			}

			$setting_id = sprintf( 'nav_menu_locations[%s]', $nav_menu_location );
			if ( empty( $changeset_data[ $setting_id ] ) || ! empty( $changeset_data[ $setting_id ]['starter_content'] ) ) {
				$this->set_post_value( $setting_id, $nav_menu_term_id );
				$this->pending_starter_content_settings_ids[] = $setting_id;
			}
		}

		// Options.
		foreach ( $options as $name => $value ) {

			// Serialize the value to check for post symbols.
			$value = maybe_serialize( $value );

			if ( is_serialized( $value ) ) {
				if ( preg_match( '/s:\d+:"{{(?P<symbol>.+)}}"/', $value, $matches ) ) {
					if ( isset( $posts[ $matches['symbol'] ] ) ) {
						$symbol_match = $posts[ $matches['symbol'] ]['ID'];
					} elseif ( isset( $attachment_ids[ $matches['symbol'] ] ) ) {
						$symbol_match = $attachment_ids[ $matches['symbol'] ];
					}

					// If we have any symbol matches, update the values.
					if ( isset( $symbol_match ) ) {
						// Replace found string matches with post IDs.
						$value = str_replace( $matches[0], "i:{$symbol_match}", $value );
					} else {
						continue;
					}
				}
			} elseif ( preg_match( '/^{{(?P<symbol>.+)}}$/', $value, $matches ) ) {
				if ( isset( $posts[ $matches['symbol'] ] ) ) {
					$value = $posts[ $matches['symbol'] ]['ID'];
				} elseif ( isset( $attachment_ids[ $matches['symbol'] ] ) ) {
					$value = $attachment_ids[ $matches['symbol'] ];
				} else {
					continue;
				}
			}

			// Unserialize values after checking for post symbols, so they can be properly referenced.
			$value = maybe_unserialize( $value );

			if ( empty( $changeset_data[ $name ] ) || ! empty( $changeset_data[ $name ]['starter_content'] ) ) {
				$this->set_post_value( $name, $value );
				$this->pending_starter_content_settings_ids[] = $name;
			}
		}

		// Theme mods.
		foreach ( $theme_mods as $name => $value ) {

			// Serialize the value to check for post symbols.
			$value = maybe_serialize( $value );

			// Check if value was serialized.
			if ( is_serialized( $value ) ) {
				if ( preg_match( '/s:\d+:"{{(?P<symbol>.+)}}"/', $value, $matches ) ) {
					if ( isset( $posts[ $matches['symbol'] ] ) ) {
						$symbol_match = $posts[ $matches['symbol'] ]['ID'];
					} elseif ( isset( $attachment_ids[ $matches['symbol'] ] ) ) {
						$symbol_match = $attachment_ids[ $matches['symbol'] ];
					}

					// If we have any symbol matches, update the values.
					if ( isset( $symbol_match ) ) {
						// Replace found string matches with post IDs.
						$value = str_replace( $matches[0], "i:{$symbol_match}", $value );
					} else {
						continue;
					}
				}
			} elseif ( preg_match( '/^{{(?P<symbol>.+)}}$/', $value, $matches ) ) {
				if ( isset( $posts[ $matches['symbol'] ] ) ) {
					$value = $posts[ $matches['symbol'] ]['ID'];
				} elseif ( isset( $attachment_ids[ $matches['symbol'] ] ) ) {
					$value = $attachment_ids[ $matches['symbol'] ];
				} else {
					continue;
				}
			}

			// Unserialize values after checking for post symbols, so they can be properly referenced.
			$value = maybe_unserialize( $value );

			// Handle header image as special case since setting has a legacy format.
			if ( 'header_image' === $name ) {
				$name     = 'header_image_data';
				$metadata = wp_get_attachment_metadata( $value );
				if ( empty( $metadata ) ) {
					continue;
				}
				$value = array(
					'attachment_id' => $value,
					'url'           => wp_get_attachment_url( $value ),
					'height'        => $metadata['height'],
					'width'         => $metadata['width'],
				);
			} elseif ( 'background_image' === $name ) {
				$value = wp_get_attachment_url( $value );
			}

			if ( empty( $changeset_data[ $name ] ) || ! empty( $changeset_data[ $name ]['starter_content'] ) ) {
				$this->set_post_value( $name, $value );
				$this->pending_starter_content_settings_ids[] = $name;
			}
		}

		if ( ! empty( $this->pending_starter_content_settings_ids ) ) {
			if ( did_action( 'customize_register' ) ) {
				$this->_save_starter_content_changeset();
			} else {
				add_action( 'customize_register', array( $this, '_save_starter_content_changeset' ), 1000 );
			}
		}
	}