diff --git a/src/wp-admin/includes/bookmark.php b/src/wp-admin/includes/bookmark.php
index c64bac144c588..eefb05df464de 100644
--- a/src/wp-admin/includes/bookmark.php
+++ b/src/wp-admin/includes/bookmark.php
@@ -121,10 +121,13 @@ function wp_delete_link( $link_id ) {
  * @since 2.1.0
  *
  * @param int $link_id Link ID to look up.
- * @return int[] The IDs of the requested link's categories.
+ * @return int[]|WP_Error The IDs of the requested link's categories, or else a WP_Error if the `link_category` taxonomy was unregistered.
  */
 function wp_get_link_cats( $link_id = 0 ) {
 	$cats = wp_get_object_terms( $link_id, 'link_category', array( 'fields' => 'ids' ) );
+	if ( is_wp_error( $cats ) ) {
+		return $cats;
+	}
 	return array_unique( $cats );
 }
 
@@ -170,6 +173,8 @@ function get_link_to_edit( $link ) {
  * }
  * @param bool  $wp_error Optional. Whether to return a WP_Error object on failure. Default false.
  * @return int|WP_Error The link ID on success. The value 0 or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? int<0, max> : int<0, max>|WP_Error )
  */
 function wp_insert_link( $linkdata, $wp_error = false ) {
 	global $wpdb;
diff --git a/src/wp-admin/includes/menu.php b/src/wp-admin/includes/menu.php
index a95cf9e33956e..f1c2985e93e8e 100644
--- a/src/wp-admin/includes/menu.php
+++ b/src/wp-admin/includes/menu.php
@@ -208,6 +208,10 @@
  * @param string $class_to_add The CSS class to add.
  * @param string $classes      The string to add the CSS class to.
  * @return string The string with the CSS class added.
+ *
+ * @phpstan-template T of string
+ * @phpstan-param T $class_to_add
+ * @phpstan-return ( $classes is empty ? T : non-empty-string )
  */
 function add_cssclass( $class_to_add, $classes ) {
 	if ( empty( $classes ) ) {
diff --git a/src/wp-admin/includes/plugin.php b/src/wp-admin/includes/plugin.php
index 53d933d07e4d8..a34d473bca650 100644
--- a/src/wp-admin/includes/plugin.php
+++ b/src/wp-admin/includes/plugin.php
@@ -906,6 +906,8 @@ function activate_plugins( $plugins, $redirect = '', $network_wide = false, $sil
  * @param string   $deprecated Not used.
  * @return bool|null|WP_Error True on success, false if `$plugins` is empty, `WP_Error` on failure.
  *                            `null` if filesystem credentials are required to proceed.
+ *
+ * @phpstan-return ( $plugins is empty ? false : true|null|WP_Error )
  */
 function delete_plugins( $plugins, $deprecated = '' ) {
 	global $wp_filesystem;
@@ -1111,6 +1113,8 @@ function validate_active_plugins() {
  *
  * @param string $plugin Path to the plugin file relative to the plugins directory.
  * @return int|WP_Error 0 on success, WP_Error on failure.
+ *
+ * @phpstan-return ( $plugin is empty ? WP_Error : 0|WP_Error )
  */
 function validate_plugin( $plugin ) {
 	if ( validate_file( $plugin ) ) {
diff --git a/src/wp-admin/includes/taxonomy.php b/src/wp-admin/includes/taxonomy.php
index 470d36d55ffb1..dbdab1af4fab8 100644
--- a/src/wp-admin/includes/taxonomy.php
+++ b/src/wp-admin/includes/taxonomy.php
@@ -117,6 +117,10 @@ function wp_create_categories( $categories, $post_id = 0 ) {
  * @param bool  $wp_error Optional. Default false.
  * @return int|WP_Error The ID number of the new or updated Category on success. Zero or a WP_Error on failure,
  *                      depending on param `$wp_error`.
+ *
+ * @phpstan-return (
+ *     $wp_error is false ? int : int|WP_Error
+ * )
  */
 function wp_insert_category( $catarr, $wp_error = false ) {
 	$cat_defaults = array(
@@ -218,6 +222,12 @@ function wp_update_category( $catarr ) {
  * @return mixed Returns null if the term does not exist.
  *               Returns an array of the term ID and the term taxonomy ID if the pairing exists.
  *               Returns 0 if term ID 0 is passed to the function.
+ *
+ * @phpstan-return (
+ *     $tag_name is 0
+ *         ? 0
+ *         : ( $tag_name is '' ? null : array{ term_id: string, term_taxonomy_id: string }|null )
+ * )
  */
 function tag_exists( $tag_name ) {
 	return term_exists( $tag_name, 'post_tag' );
diff --git a/src/wp-includes/block-template-utils.php b/src/wp-includes/block-template-utils.php
index 96d2372694200..78cd1bbdc15f5 100644
--- a/src/wp-includes/block-template-utils.php
+++ b/src/wp-includes/block-template-utils.php
@@ -319,8 +319,8 @@ function _get_block_templates_paths( $base_directory ) {
  * @param string $template_type Template type. Either 'wp_template' or 'wp_template_part'.
  * @param string $slug          Template slug.
  * @return array|null {
- *     Array with template metadata if $template_type is one of 'wp_template' or 'wp_template_part',
- *     null otherwise.
+ *     Array with template metadata, or null if `$template_type` is neither 'wp_template' nor
+ *     'wp_template_part', or if the theme has no template file for `$slug`.
  *
  *     @type string   $slug      Template slug.
  *     @type string   $path      Template file path.
@@ -392,6 +392,10 @@ function _get_block_template_file( $template_type, $slug ) {
  * }
  *
  * @return array|null Template files on success, null if `$template_type` is not matched.
+ *
+ * @phpstan-return (
+ *     $template_type is 'wp_template'|'wp_template_part' ? list<array<array-key, mixed>> : null
+ * )
  */
 function _get_block_templates_files( $template_type, $query = array() ) {
 	if ( 'wp_template' !== $template_type && 'wp_template_part' !== $template_type ) {
diff --git a/src/wp-includes/blocks.php b/src/wp-includes/blocks.php
index 487c2765ac249..beaf08d4022c6 100644
--- a/src/wp-includes/blocks.php
+++ b/src/wp-includes/blocks.php
@@ -2682,6 +2682,8 @@ function _wp_apply_block_content_filters( $content, $context = '', &$seen_ids =
  *
  * @param string $content Content to test.
  * @return int The block format version is 1 if the content contains one or more blocks, 0 otherwise.
+ *
+ * @phpstan-return ( $content is '' ? 0 : 0|1 )
  */
 function block_version( $content ) {
 	return has_blocks( $content ) ? 1 : 0;
diff --git a/src/wp-includes/bookmark.php b/src/wp-includes/bookmark.php
index 9e44d781909ed..e1c8a6e522a00 100644
--- a/src/wp-includes/bookmark.php
+++ b/src/wp-includes/bookmark.php
@@ -20,6 +20,13 @@
  *                               respectively. Default OBJECT.
  * @param string       $filter   Optional. How to sanitize bookmark fields. Default 'raw'.
  * @return array|object|null Type returned depends on $output value.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return null|(
+ *     $output is 'ARRAY_A' ? array<string, mixed> : (
+ *         $output is 'ARRAY_N' ? array<int, mixed> : stdClass
+ *     )
+ * )
  */
 function get_bookmark( $bookmark, $output = OBJECT, $filter = 'raw' ) {
 	global $wpdb;
diff --git a/src/wp-includes/category-template.php b/src/wp-includes/category-template.php
index f268f93cbc461..1d456f309de3d 100644
--- a/src/wp-includes/category-template.php
+++ b/src/wp-includes/category-template.php
@@ -534,6 +534,8 @@ function wp_dropdown_categories( $args = '' ) {
  * }
  * @return void|string|false Void if 'echo' argument is true, HTML list of categories if 'echo' is false.
  *                           False if the taxonomy does not exist.
+ *
+ * @phpstan-return ( $args is array{ echo: false|0, ... } ? string|false : false|void )
  */
 function wp_list_categories( $args = '' ) {
 	$defaults = array(
@@ -849,6 +851,8 @@ function default_topic_count_scale( $count ) {
  *                                                0, 1, or their bool equivalents.
  * }
  * @return string|string[] Tag cloud as a string or an array, depending on 'format' argument.
+ *
+ * @phpstan-return ( $args is array{ format: 'array', ... } ? array<int, string> : string )
  */
 function wp_generate_tag_cloud( $tags, $args = '' ) {
 	$defaults = array(
diff --git a/src/wp-includes/category.php b/src/wp-includes/category.php
index dbb48d630b076..6f35c5db0bbf4 100644
--- a/src/wp-includes/category.php
+++ b/src/wp-includes/category.php
@@ -22,6 +22,24 @@
  *     @type string $taxonomy Taxonomy to retrieve terms for. Default 'category'.
  * }
  * @return array List of category objects.
+ *
+ * @phpstan-return (
+ *     $args is array{ fields: 'count', ... }
+ *         ? list<numeric-string>
+ *         : (
+ *             $args is array{ fields: 'names'|'slugs', ... }
+ *                 ? list<string>
+ *                 : (
+ *                     $args is array{ fields: 'id=>name'|'id=>slug', ... }
+ *                         ? array<int, string>
+ *                         : (
+ *                             $args is array{ fields: 'id=>parent', ... }
+ *                                 ? array<int, int>
+ *                                 : ( $args is array{ fields: 'ids'|'tt_ids', ... } ? list<int> : array<int, WP_Term> )
+ *                         )
+ *                 )
+ *         )
+ * )
  */
 function get_categories( $args = '' ) {
 	$defaults = array( 'taxonomy' => 'category' );
@@ -88,6 +106,13 @@ function get_categories( $args = '' ) {
  * @return WP_Term|array|WP_Error|null Category data in type defined by $output parameter.
  *                                     Returns a WP_Term object with backwards compatible property aliases filled in.
  *                                     WP_Error if $category is empty, null if it does not exist.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? array<string, mixed>|WP_Error|null : (
+ *         $output is 'ARRAY_N' ? list<mixed>|WP_Error|null : WP_Term|WP_Error|null
+ *     )
+ * )
  */
 function get_category( $category, $output = OBJECT, $filter = 'raw' ) {
 	$category = get_term( $category, 'category', $output, $filter );
@@ -121,6 +146,13 @@ function get_category( $category, $output = OBJECT, $filter = 'raw' ) {
  *                              correspond to a WP_Term object, an associative array, or a numeric array,
  *                              respectively. Default OBJECT.
  * @return WP_Term|array|WP_Error|null Type is based on $output value.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? array<string, mixed>|WP_Error|null : (
+ *         $output is 'ARRAY_N' ? list<mixed>|WP_Error|null : WP_Term|WP_Error|null
+ *     )
+ * )
  */
 function get_category_by_path( $category_path, $full_match = true, $output = OBJECT ) {
 	$category_path  = rawurlencode( urldecode( $category_path ) );
@@ -293,6 +325,20 @@ function sanitize_category_field( $field, $value, $cat_id, $context ) {
  * }
  * @return WP_Term[]|int|WP_Error Array of 'post_tag' term objects, a count thereof,
  *                                or WP_Error if any of the taxonomies do not exist.
+ *
+ * @phpstan-return (
+ *     $args is array{ fields: 'names'|'slugs', ... }
+ *         ? list<string>
+ *         : (
+ *             $args is array{ fields: 'id=>name'|'id=>slug', ... }
+ *                 ? array<int, string>
+ *                 : (
+ *                     $args is array{ fields: 'id=>parent', ... }
+ *                         ? array<int, int>
+ *                         : ( $args is array{ fields: 'ids'|'tt_ids', ... } ? list<int> : array<int, WP_Term> )
+ *                 )
+ *         )
+ * )|WP_Error
  */
 function get_tags( $args = '' ) {
 	$defaults = array( 'taxonomy' => 'post_tag' );
@@ -339,6 +385,13 @@ function get_tags( $args = '' ) {
  * @param string             $filter Optional. How to sanitize tag fields. Default 'raw'.
  * @return WP_Term|array|WP_Error|null Tag data in type defined by $output parameter.
  *                                     WP_Error if $tag is empty, null if it does not exist.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? array<string, mixed>|WP_Error|null : (
+ *         $output is 'ARRAY_N' ? list<mixed>|WP_Error|null : WP_Term|WP_Error|null
+ *     )
+ * )
  */
 function get_tag( $tag, $output = OBJECT, $filter = 'raw' ) {
 	return get_term( $tag, 'post_tag', $output, $filter );
diff --git a/src/wp-includes/class-wp-block-supports.php b/src/wp-includes/class-wp-block-supports.php
index cf2d84f3b6756..c065cd911de04 100644
--- a/src/wp-includes/class-wp-block-supports.php
+++ b/src/wp-includes/class-wp-block-supports.php
@@ -197,6 +197,8 @@ private function register_attributes() {
  *
  * @param string[] $extra_attributes Optional. Array of extra attributes to render on the block wrapper.
  * @return string String of HTML attributes.
+ *
+ * @phpstan-return ( $extra_attributes is empty ? string : non-falsy-string )
  */
 function get_block_wrapper_attributes( $extra_attributes = array() ) {
 	$new_attributes = WP_Block_Supports::get_instance()->apply_block_supports();
diff --git a/src/wp-includes/class-wp-comment-query.php b/src/wp-includes/class-wp-comment-query.php
index f80864d31c8bc..a82cd5cd22372 100644
--- a/src/wp-includes/class-wp-comment-query.php
+++ b/src/wp-includes/class-wp-comment-query.php
@@ -365,7 +365,12 @@ public function parse_query( $query = '' ) {
 	 *
 	 * @param string|array $query Array or URL query string of parameters.
 	 * @return WP_Comment[]|int[]|int List of comments, or number of comments when 'count' is passed as a query var.
-	 * @phpstan-return array<int, WP_Comment>|non-negative-int[]|non-negative-int
+	 *
+	 * @phpstan-return (
+	 *     $query is array{ count: true, ... } ? non-negative-int : (
+	 *         $query is array{ fields: 'ids', ... } ? non-negative-int[] : array<int, WP_Comment>
+	 *     )
+	 * )
 	 */
 	public function query( $query ) {
 		$this->query_vars = wp_parse_args( $query );
diff --git a/src/wp-includes/class-wp-dependencies.php b/src/wp-includes/class-wp-dependencies.php
index c2daba389bd75..167dfd692ef70 100644
--- a/src/wp-includes/class-wp-dependencies.php
+++ b/src/wp-includes/class-wp-dependencies.php
@@ -472,6 +472,16 @@ protected function recurse_deps( $queue, $handle ) {
 	 * @param string $handle Name of the item. Should be unique.
 	 * @param string $status Optional. Status of the item to query. Default 'registered'.
 	 * @return bool|_WP_Dependency Found, or object Item data.
+	 *
+	 * @phpstan-return (
+	 *     $handle is not non-empty-string
+	 *         ? false
+	 *         : (
+	 *             $status is not 'registered'|'scripts'|'enqueued'|'queued'|'to_do'|'to_print'|'done'|'printed'
+	 *                 ? false
+	 *                 : ( $status is 'registered'|'scripts' ? _WP_Dependency|false : bool )
+	 *         )
+	 * )
 	 */
 	public function query( $handle, $status = 'registered' ) {
 		switch ( $status ) {
diff --git a/src/wp-includes/class-wp-hook.php b/src/wp-includes/class-wp-hook.php
index 1718878308300..9a4d4a2c5eeca 100644
--- a/src/wp-includes/class-wp-hook.php
+++ b/src/wp-includes/class-wp-hook.php
@@ -250,6 +250,13 @@ public function remove_filter( $hook_name, $callback, $priority ) {
 	 *                  If `$callback` and `$priority` are both provided, a boolean is returned
 	 *                  for whether the specific function is registered at that priority.
 	 * @phpstan-param Maybe_Callable|false $callback
+	 * @phpstan-return (
+	 *     $callback is false
+	 *         ? bool
+	 *         : ( $priority is int
+	 *             ? bool
+	 *             : false|int )
+	 * )
 	 */
 	public function has_filter( $hook_name = '', $callback = false, $priority = false ) {
 		if ( false === $callback ) {
diff --git a/src/wp-includes/class-wp-network-query.php b/src/wp-includes/class-wp-network-query.php
index 7a5e9e7f41ffc..a7c747798f930 100644
--- a/src/wp-includes/class-wp-network-query.php
+++ b/src/wp-includes/class-wp-network-query.php
@@ -179,8 +179,14 @@ public function parse_query( $query = '' ) {
 	 * @since 4.6.0
 	 *
 	 * @param string|array $query Array or URL query string of parameters.
-	 * @return array|int List of WP_Network objects, a list of network IDs when 'fields' is set to 'ids',
-	 *                   or the number of networks when 'count' is passed as a query var.
+	 * @return WP_Network[]|int[]|int List of WP_Network objects, a list of network IDs when 'fields' is set
+	 *                                to 'ids', or the number of networks when 'count' is passed as a query var.
+	 *
+	 * @phpstan-return (
+	 *     $query is array{ count: true, ... } ? int : (
+	 *         $query is array{ fields: 'ids', ... } ? int[] : array<int, WP_Network>
+	 *     )
+	 * )
 	 */
 	public function query( $query ) {
 		$this->query_vars = wp_parse_args( $query );
@@ -192,8 +198,8 @@ public function query( $query ) {
 	 *
 	 * @since 4.6.0
 	 *
-	 * @return array|int List of WP_Network objects, a list of network IDs when 'fields' is set to 'ids',
-	 *                   or the number of networks when 'count' is passed as a query var.
+	 * @return WP_Network[]|int[]|int List of WP_Network objects, a list of network IDs when 'fields' is set
+	 *                                to 'ids', or the number of networks when 'count' is passed as a query var.
 	 */
 	public function get_networks() {
 		$this->parse_query();
@@ -234,10 +240,11 @@ public function get_networks() {
 		 * @since 5.6.0 The returned array of network data is assigned to the `networks` property
 		 *              of the current WP_Network_Query instance.
 		 *
-		 * @param array|int|null   $network_data Return an array of network data to short-circuit WP's network query,
-		 *                                       the network count as an integer if `$this->query_vars['count']` is set,
-		 *                                       or null to allow WP to run its normal queries.
-		 * @param WP_Network_Query $query        The WP_Network_Query instance, passed by reference.
+		 * @param WP_Network[]|int[]|int|null $network_data Return an array of network data to short-circuit WP's
+		 *                                                  network query, the network count as an integer if
+		 *                                                  `$this->query_vars['count']` is set, or null to allow WP
+		 *                                                  to run its normal queries.
+		 * @param WP_Network_Query            $query        The WP_Network_Query instance, passed by reference.
 		 */
 		$network_data = apply_filters_ref_array( 'networks_pre_query', array( $network_data, &$this ) );
 
diff --git a/src/wp-includes/class-wp-site-query.php b/src/wp-includes/class-wp-site-query.php
index 52ae228d90af0..aab8b511fcf83 100644
--- a/src/wp-includes/class-wp-site-query.php
+++ b/src/wp-includes/class-wp-site-query.php
@@ -265,6 +265,12 @@ public function parse_query( $query = '' ) {
 	 * @param string|array $query Array or URL query string of parameters.
 	 * @return WP_Site[]|int[]|int List of WP_Site objects, a list of site IDs when 'fields' is set to 'ids',
 	 *                             or the number of sites when 'count' is passed as a query var.
+	 *
+	 * @phpstan-return (
+	 *     $query is array{ count: true, ... } ? int : (
+	 *         $query is array{ fields: 'ids', ... } ? int[] : array<int, WP_Site>
+	 *     )
+	 * )
 	 */
 	public function query( $query ) {
 		$this->query_vars = wp_parse_args( $query );
diff --git a/src/wp-includes/class-wp-term.php b/src/wp-includes/class-wp-term.php
index 33547e4cbef98..a9a58da875e4a 100644
--- a/src/wp-includes/class-wp-term.php
+++ b/src/wp-includes/class-wp-term.php
@@ -225,7 +225,7 @@ public function filter( $filter ) {
 	 *
 	 * @since 4.4.0
 	 *
-	 * @return array Object as array.
+	 * @return array<string, mixed> Object as array.
 	 */
 	public function to_array() {
 		return get_object_vars( $this );
diff --git a/src/wp-includes/class-wp-theme.php b/src/wp-includes/class-wp-theme.php
index 87399e399a198..87fcd7eec72b4 100644
--- a/src/wp-includes/class-wp-theme.php
+++ b/src/wp-includes/class-wp-theme.php
@@ -5,6 +5,8 @@
  * @package WordPress
  * @subpackage Theme
  * @since 3.4.0
+ *
+ * @phpstan-type Theme_Key 'Name'|'Version'|'Status'|'Title'|'Author'|'Author Name'|'Author URI'|'Description'|'Template'|'Stylesheet'|'Template Files'|'Stylesheet Files'|'Template Dir'|'Stylesheet Dir'|'Screenshot'|'Tags'|'Theme Root'|'Theme Root URI'|'Parent Theme'
  */
 #[AllowDynamicProperties]
 final class WP_Theme implements ArrayAccess {
@@ -654,6 +656,8 @@ public function offsetUnset( $offset ) {}
 	 *
 	 * @param mixed $offset
 	 * @return bool
+	 *
+	 * @phpstan-return ( $offset is Theme_Key ? true : false )
 	 */
 	#[ReturnTypeWillChange]
 	public function offsetExists( $offset ) {
@@ -696,6 +700,8 @@ public function offsetExists( $offset ) {
 	 *
 	 * @param mixed $offset
 	 * @return mixed
+	 *
+	 * @phpstan-return ( $offset is Theme_Key ? mixed : null )
 	 */
 	#[ReturnTypeWillChange]
 	public function offsetGet( $offset ) {
@@ -916,6 +922,14 @@ public function get( $header ) {
 	 * @param bool   $translate Optional. Whether to translate the header. Defaults to true.
 	 * @return string|array|false Processed header. An array for Tags if `$markup` is false, string otherwise.
 	 *                            False on failure.
+	 *
+	 * @phpstan-return (
+	 *     $markup is false
+	 *         ? ( $header is 'Tags'
+	 *             ? string[]|false
+	 *             : string|false )
+	 *         : string|false
+	 * )
 	 */
 	public function display( $header, $markup = true, $translate = true ) {
 		$value = $this->get( $header );
@@ -949,7 +963,9 @@ public function display( $header, $markup = true, $translate = true ) {
 	 *                       'ThemeURI', 'AuthorURI', 'Status', 'Tags', 'RequiresWP', 'RequiresPHP',
 	 *                       'UpdateURI'.
 	 * @param string $value  Value to sanitize.
-	 * @return string|array An array for Tags header, string otherwise.
+	 * @return string|string[] An array for Tags header, string otherwise.
+	 *
+	 * @phpstan-return ( $header is 'Tags' ? string[] : string )
 	 */
 	private function sanitize_header( $header, $value ) {
 		switch ( $header ) {
@@ -1053,9 +1069,11 @@ private function markup_header( $header, $value, $translate ) {
 	 *
 	 * @since 3.4.0
 	 *
-	 * @param string       $header Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
-	 * @param string|array $value  Value to translate. An array for Tags header, string otherwise.
-	 * @return string|array Translated value. An array for Tags header, string otherwise.
+	 * @param string          $header Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
+	 * @param string|string[] $value  Value to translate. An array for Tags header, string otherwise.
+	 * @return string|string[] Translated value. An array for Tags header, string otherwise.
+	 *
+	 * @phpstan-return ( $value is string ? string : string[] )
 	 */
 	private function translate_header( $header, $value ) {
 		switch ( $header ) {
diff --git a/src/wp-includes/class-wp-user-query.php b/src/wp-includes/class-wp-user-query.php
index 3815023924489..61fc3edbc8ef9 100644
--- a/src/wp-includes/class-wp-user-query.php
+++ b/src/wp-includes/class-wp-user-query.php
@@ -962,7 +962,8 @@ protected function get_search_sql( $search, $columns, $wild = false ) {
 	 *
 	 * @since 3.1.0
 	 *
-	 * @return array Array of results.
+	 * @return array<int, mixed> Array of results. Contains WP_User objects unless the 'fields' query var
+	 *                           requested specific fields, in which case it contains the requested values.
 	 */
 	public function get_results() {
 		return $this->results;
diff --git a/src/wp-includes/comment.php b/src/wp-includes/comment.php
index 03511ee4db709..239435dc308a3 100644
--- a/src/wp-includes/comment.php
+++ b/src/wp-includes/comment.php
@@ -762,6 +762,10 @@ function sanitize_comment_cookies() {
  *                           Default false.
  * @return int|string|WP_Error Allowed comments return the approval status (0|1|'spam'|'trash').
  *                             If `$wp_error` is true, disallowed comments return a WP_Error.
+ *
+ * @phpstan-return (
+ *     $wp_error is false ? int|string : int|string|WP_Error
+ * )
  */
 function wp_allow_comment( $commentdata, $wp_error = false ) {
 	global $wpdb;
@@ -2805,6 +2809,8 @@ function wp_send_note_notification( WP_User $user, WP_Comment $comment, ?WP_Post
  * @param string         $comment_status New comment status, either 'hold', 'approve', 'spam', or 'trash'.
  * @param bool           $wp_error       Whether to return a WP_Error object if there is a failure. Default false.
  * @return bool|WP_Error True on success, false or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? bool : true|WP_Error )
  */
 function wp_set_comment_status( $comment_id, $comment_status, $wp_error = false ) {
 	global $wpdb;
@@ -2879,6 +2885,8 @@ function wp_set_comment_status( $comment_id, $comment_status, $wp_error = false
  * @param bool  $wp_error   Optional. Whether to return a WP_Error on failure. Default false.
  * @return int|false|WP_Error The value 1 if the comment was updated, 0 if not updated.
  *                            False or a WP_Error object on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? int|false : int|WP_Error )
  */
 function wp_update_comment( $commentarr, $wp_error = false ) {
 	global $wpdb;
diff --git a/src/wp-includes/cron.php b/src/wp-includes/cron.php
index 1070ae4680b91..743b37b326b25 100644
--- a/src/wp-includes/cron.php
+++ b/src/wp-includes/cron.php
@@ -44,6 +44,8 @@
  *                           database performance issues.
  * @param bool   $wp_error   Optional. Whether to return a WP_Error on failure. Default false.
  * @return bool|WP_Error True if event successfully scheduled. False or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? bool : true|WP_Error )
  */
 function wp_schedule_single_event( $timestamp, $hook, $args = array(), $wp_error = false ) {
 	// Make sure timestamp is a positive integer.
@@ -248,6 +250,8 @@ function wp_schedule_single_event( $timestamp, $hook, $args = array(), $wp_error
  *                           database performance issues.
  * @param bool   $wp_error   Optional. Whether to return a WP_Error on failure. Default false.
  * @return bool|WP_Error True if event successfully scheduled. False or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? bool : true|WP_Error )
  */
 function wp_schedule_event( $timestamp, $recurrence, $hook, $args = array(), $wp_error = false ) {
 	// Make sure timestamp is a positive integer.
@@ -363,6 +367,8 @@ function wp_schedule_event( $timestamp, $recurrence, $hook, $args = array(), $wp
  *                           database performance issues.
  * @param bool   $wp_error   Optional. Whether to return a WP_Error on failure. Default false.
  * @return bool|WP_Error True if event successfully rescheduled. False or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? bool : true|WP_Error )
  */
 function wp_reschedule_event( $timestamp, $recurrence, $hook, $args = array(), $wp_error = false ) {
 	// Make sure timestamp is a positive integer.
@@ -485,6 +491,8 @@ function wp_reschedule_event( $timestamp, $recurrence, $hook, $args = array(), $
  *                          arguments do not match exactly, the event will not be found. Default empty array.
  * @param bool   $wp_error  Optional. Whether to return a WP_Error on failure. Default false.
  * @return bool|WP_Error True if event successfully unscheduled. False or WP_Error on failure.
+ *
+ * @phpstan-return ( $wp_error is false ? bool : true|WP_Error )
  */
 function wp_unschedule_event( $timestamp, $hook, $args = array(), $wp_error = false ) {
 	// Make sure timestamp is a positive integer.
@@ -572,6 +580,8 @@ function wp_unschedule_event( $timestamp, $hook, $args = array(), $wp_error = fa
  * @return int|false|WP_Error On success an integer indicating number of events unscheduled (0 indicates no
  *                            events were registered with the hook and arguments combination), false or WP_Error
  *                            if unscheduling one or more events fail.
+ *
+ * @phpstan-return ( int|( $wp_error is false ? false : WP_Error ) )
  */
 function wp_clear_scheduled_hook( $hook, $args = array(), $wp_error = false ) {
 	/*
@@ -677,6 +687,8 @@ function wp_clear_scheduled_hook( $hook, $args = array(), $wp_error = false ) {
  * @param bool   $wp_error Optional. Whether to return a WP_Error on failure. Default false.
  * @return int|false|WP_Error On success an integer indicating number of events unscheduled (0 indicates no
  *                            events were registered on the hook), false or WP_Error if unscheduling fails.
+ *
+ * @phpstan-return ( $wp_error is false ? int|false : int|WP_Error )
  */
 function wp_unschedule_hook( $hook, $wp_error = false ) {
 	/**
diff --git a/src/wp-includes/deprecated.php b/src/wp-includes/deprecated.php
index 3b78d1610fdad..75d064c414ee2 100644
--- a/src/wp-includes/deprecated.php
+++ b/src/wp-includes/deprecated.php
@@ -2021,7 +2021,15 @@ function get_attachment_innerHTML($id = 0, $fullsize = false, $max_dims = false)
  *                            Default OBJECT.
  * @param string $filter      Optional. How to filter the link for output. Accepts 'raw', 'edit',
  *                            'attribute', 'js', 'db', or 'display'. Default 'raw'.
- * @return object|array Bookmark object or array, depending on the type specified by `$output`.
+ * @return object|array|null Bookmark object or array, depending on the type specified by `$output`.
+ *                            Null if the bookmark does not exist.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return null|(
+ *     $output is 'ARRAY_A' ? array<string, mixed> : (
+ *         $output is 'ARRAY_N' ? array<int, mixed> : stdClass
+ *     )
+ * )
  */
 function get_link( $bookmark_id, $output = OBJECT, $filter = 'raw' ) {
 	_deprecated_function( __FUNCTION__, '2.1.0', 'get_bookmark()' );
@@ -2518,6 +2526,16 @@ function is_taxonomy( $taxonomy ) {
  * @param string $taxonomy The taxonomy name to use
  * @param int $parent ID of parent term under which to confine the exists search.
  * @return mixed Get the term ID or term object, if exists.
+ *
+ * @phpstan-return (
+ *     $term is 0
+ *         ? 0
+ *         : (
+ *             $term is ''
+ *                 ? null
+ *                 : ( $taxonomy is '' ? string|null : array{ term_id: string, term_taxonomy_id: string }|null )
+ *         )
+ * )
  */
 function is_term( $term, $taxonomy = '', $parent = 0 ) {
 	_deprecated_function( __FUNCTION__, '3.0.0', 'term_exists()' );
@@ -4569,6 +4587,13 @@ function _filter_query_attachment_filenames( $clauses ) {
  *                                 respectively. Default OBJECT.
  * @param string|array $post_type  Optional. Post type or array of post types. Default 'page'.
  * @return WP_Post|array|null WP_Post (or array) on success, or null on failure.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? non-empty-array<string, mixed>|null : (
+ *         $output is 'ARRAY_N' ? non-empty-array<int, mixed>|null : WP_Post|null
+ *     )
+ * )
  */
 function get_page_by_title( $page_title, $output = OBJECT, $post_type = 'page' ) {
 	_deprecated_function( __FUNCTION__, '6.2.0', 'WP_Query' );
@@ -6498,6 +6523,8 @@ function wp_print_auto_sizes_contain_css_fix() {
  *
  * @param string|array $gpc String or array of data to slash.
  * @return string|array Slashed `$gpc`.
+ *
+ * @phpstan-return ( $gpc is string ? string : array )
  */
 function addslashes_gpc( $gpc ) {
 	_deprecated_function( __FUNCTION__, '7.0.0', 'wp_slash()' );
diff --git a/src/wp-includes/embed.php b/src/wp-includes/embed.php
index e87cf4ec57989..6a7501027a978 100644
--- a/src/wp-includes/embed.php
+++ b/src/wp-includes/embed.php
@@ -676,7 +676,7 @@ function get_oembed_response_data_for_url( $url, $args ) {
 		}
 
 		if ( $site && get_current_blog_id() !== (int) $site->blog_id ) {
-			switch_to_blog( $site->blog_id );
+			switch_to_blog( (int) $site->blog_id );
 			$switched_blog = true;
 		}
 	}
diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index 5bf001c430a49..123885663ba85 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -2412,6 +2412,10 @@ function sanitize_title_with_dashes( $title, $raw_title = '', $context = 'displa
  *
  * @param string $orderby Order by clause to be validated.
  * @return string|false Returns $orderby if valid, false otherwise.
+ *
+ * @phpstan-template T of string
+ * @phpstan-param T $orderby
+ * @phpstan-return ( T is non-empty-string ? T|false : false )
  */
 function sanitize_sql_orderby( $orderby ) {
 	if ( preg_match( '/^\s*(([a-z0-9_]+|`[a-z0-9_]+`)(\s+(ASC|DESC))?\s*(,\s*(?=[a-z0-9_`])|$))+$/i', $orderby ) || preg_match( '/^\s*RAND\(\s*\)\s*$/i', $orderby ) ) {
@@ -2788,6 +2792,16 @@ function format_to_edit( $content, $rich_text = false ) {
  * @param int $number     Number to append zeros to if not greater than threshold.
  * @param int $threshold  Digit places number needs to be to not have zeros added.
  * @return string Adds leading zeros to number if needed.
+ *
+ * @phpstan-return (
+ *     $threshold is 0
+ *         ? lowercase-string&non-empty-string&numeric-string
+ *         : (
+ *             $number is int<0, max>
+ *                 ? lowercase-string&non-empty-string&numeric-string
+ *                 : lowercase-string&non-empty-string
+ *         )
+ * )
  */
 function zeroise( $number, $threshold ) {
 	return sprintf( '%0' . $threshold . 's', $number );
diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 89d27f75e9f58..e8932d383b503 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -31,6 +31,8 @@
  * @param bool   $translate Whether the return date should be translated. Default true.
  * @return string|int|false Integer if `$format` is 'U' or 'G', string otherwise.
  *                          False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function mysql2date( $format, $date, $translate = true ) {
 	if ( empty( $date ) ) {
@@ -74,6 +76,8 @@ function mysql2date( $format, $date, $translate = true ) {
  *                     or PHP date format string (e.g. 'Y-m-d').
  * @param bool   $gmt  Optional. Whether to use GMT timezone. Default false.
  * @return int|string Integer if `$type` is 'timestamp' or 'U', string otherwise.
+ *
+ * @phpstan-return ( $type is 'timestamp'|'U' ? int : string )
  */
 function current_time( $type, $gmt = false ) {
 	// Don't use non-GMT timestamp, unless you know the difference and really need to.
@@ -465,6 +469,8 @@ function number_format_i18n( $number, $decimals = 0 ) {
  * @return string|false Number string on success, false on failure.
  *
  * @phpstan-param int|float|numeric-string $bytes
+ *
+ * @phpstan-return ( $bytes is int<0, max> ? string : string|false )
  */
 function size_format( $bytes, $decimals = 0 ) {
 	if ( ! is_numeric( $bytes ) ) {
@@ -632,6 +638,10 @@ function get_weekstartend( $mysqlstring, $start_of_week = '' ) {
  *
  * @param string|array|object $data Data that might be serialized.
  * @return mixed A scalar data.
+ *
+ * @phpstan-template T of mixed
+ * @phpstan-param T $data
+ * @phpstan-return ( T is array|object|string ? string : T )
  */
 function maybe_serialize( $data ) {
 	if ( is_array( $data ) || is_object( $data ) ) {
@@ -840,6 +850,8 @@ function xmlrpc_removepostdata( $content ) {
  *
  * @param string $content Content to extract URLs from.
  * @return string[] Array of URLs found in passed string.
+ *
+ * @phpstan-return ( $content is empty ? array{} : list<string> )
  */
 function wp_extract_urls( $content ) {
 	preg_match_all(
@@ -1600,6 +1612,8 @@ function get_num_queries() {
  *
  * @param string $yn Character string containing either 'y' (yes) or 'n' (no).
  * @return bool True if 'y', false on anything else.
+ *
+ * @phpstan-return ( $yn is 'y' ? true : false )
  */
 function bool_from_yn( $yn ) {
 	return ( 'y' === strtolower( $yn ) );
@@ -2131,6 +2145,8 @@ function wp_mkdir_p( $target ) {
  *
  * @param string $path File path.
  * @return bool True if path is absolute, false is not absolute.
+ *
+ * @phpstan-return ( $path is non-falsy-string ? bool : false )
  */
 function path_is_absolute( $path ) {
 	/*
@@ -5416,6 +5432,8 @@ function _wp_to_kebab_case( $input_string ) {
  * @return bool Whether the variable is a list.
  *
  * @phpstan-assert-if-true array<int, mixed> $data
+ *
+ * @phpstan-return ( $data is array<int, mixed> ? true : false )
  */
 function wp_is_numeric_array( $data ): bool {
 	if ( ! is_array( $data ) ) {
@@ -6416,6 +6434,8 @@ function iis7_supports_permalinks() {
  * @param string   $file          File path.
  * @param string[] $allowed_files Optional. Array of allowed files. Default empty array.
  * @return int 0 means nothing is wrong, greater than 0 means something was wrong.
+ *
+ * @phpstan-return ( $file is '' ? 0 : ( $allowed_files is empty ? 0|1|2 : 0|1|2|3 ) )
  */
 function validate_file( $file, $allowed_files = array() ) {
 	if ( ! is_scalar( $file ) || '' === $file ) {
@@ -7298,7 +7318,11 @@ function wp_find_hierarchy_loop( $callback, $start, $start_parent, $callback_arg
  *                                to true if you already know the given $start is part of a loop (otherwise
  *                                the returned array might include branches). Default false.
  * @return mixed Scalar ID of some arbitrary member of the loop, or array of IDs of all members of loop if
- *               $_return_loop
+ *               $_return_loop. False if no loop was found.
+ *
+ * @phpstan-return (
+ *     $_return_loop is true ? array<array-key, true>|false : mixed
+ * )
  */
 function wp_find_hierarchy_loop_tortoise_hare( $callback, $start, $override = array(), $callback_args = array(), $_return_loop = false ) {
 	$tortoise        = $start;
@@ -7426,6 +7450,8 @@ function wp_allowed_protocols() {
  *                             the raw array returned. Default true.
  * @return string|array Either a string containing a reversed comma separated trace or an array
  *                      of individual calls.
+ *
+ * @phpstan-return ( $pretty is true ? string : list<string> )
  */
 function wp_debug_backtrace_summary( $ignore_class = null, $skip_frames = 0, $pretty = true ) {
 	static $truncate_paths;
@@ -7735,6 +7761,8 @@ function wp_auth_check( $response ) {
  *
  * @param string $tag An HTML tag name. Example: 'video'.
  * @return string Tag RegEx.
+ *
+ * @phpstan-return ( $tag is ''|'0' ? '' : non-falsy-string )
  */
 function get_tag_regex( $tag ) {
 	if ( empty( $tag ) ) {
@@ -8181,6 +8209,8 @@ function wp_generate_uuid4() {
  * @param int   $version Specify which version of UUID to check against. Default is none,
  *                       to accept any UUID version. Otherwise, only version allowed is `4`.
  * @return bool The string is a valid UUID or false on failure.
+ *
+ * @phpstan-return ( $version is 4|null ? bool : false )
  */
 function wp_is_uuid( $uuid, $version = null ) {
 
@@ -8213,6 +8243,12 @@ function wp_is_uuid( $uuid, $version = null ) {
  *
  * @param string $prefix Prefix for the returned ID.
  * @return string Unique ID.
+ *
+ * @phpstan-return (
+ *     ( $prefix is ''|numeric-string ? numeric-string : string )
+ *     & non-falsy-string
+ *     & ( $prefix is lowercase-string ? lowercase-string : string )
+ * )
  */
 function wp_unique_id( $prefix = '' ) {
 	static $id_counter = 0;
@@ -8232,6 +8268,12 @@ function wp_unique_id( $prefix = '' ) {
  *
  * @param string $prefix Optional. Prefix for the returned ID. Default empty string.
  * @return string Incremental ID per prefix.
+ *
+ * @phpstan-return (
+ *     ( $prefix is ''|numeric-string ? numeric-string : string )
+ *     & non-falsy-string
+ *     & ( $prefix is lowercase-string ? lowercase-string : string )
+ * )
  */
 function wp_unique_prefixed_id( $prefix = '' ) {
 	static $id_counters = array();
@@ -8265,6 +8307,8 @@ function wp_unique_prefixed_id( $prefix = '' ) {
  * @param array  $data   The input array to generate an ID from.
  * @param string $prefix Optional. A prefix to prepend to the generated ID. Default empty string.
  * @return string The generated unique ID for the array.
+ *
+ * @phpstan-return ( $prefix is lowercase-string ? lowercase-string&non-falsy-string : non-falsy-string )
  */
 function wp_unique_id_from_values( array $data, string $prefix = '' ): string {
 	if ( empty( $data ) ) {
diff --git a/src/wp-includes/general-template.php b/src/wp-includes/general-template.php
index 2f37fbae50bbf..71c234df6612d 100644
--- a/src/wp-includes/general-template.php
+++ b/src/wp-includes/general-template.php
@@ -1929,6 +1929,8 @@ function single_term_title( $prefix = '', $display = true ) {
  * @param string $prefix  Optional. What to display before the title.
  * @param bool   $display Optional. Whether to display or retrieve title. Default true.
  * @return string|false|null False if there's no valid title for the month. Title when retrieving.
+ *
+ * @phpstan-return ( $display is true ? false|null : string|false )
  */
 function single_month_title( $prefix = '', $display = true ) {
 	global $wp_locale;
@@ -3002,6 +3004,8 @@ function the_date( $format = '', $before = '', $after = '', $display = true ) {
  * @param string           $format Optional. PHP date format. Defaults to the 'date_format' option.
  * @param int|WP_Post|null $post   Optional. Post ID or WP_Post object. Default current post.
  * @return string|int|false Date the current post was written. False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_the_date( $format = '', $post = null ) {
 	$post = get_post( $post );
@@ -3069,6 +3073,8 @@ function the_modified_date( $format = '', $before = '', $after = '', $display =
  * @param string           $format Optional. PHP date format. Defaults to the 'date_format' option.
  * @param int|WP_Post|null $post   Optional. Post ID or WP_Post object. Default current post.
  * @return string|int|false Date the current post was modified. False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_the_modified_date( $format = '', $post = null ) {
 	$post = get_post( $post );
@@ -3128,6 +3134,8 @@ function the_time( $format = '' ) {
  * @param int|WP_Post|null $post   Post ID or post object. Default is global `$post` object.
  * @return string|int|false Formatted date string or Unix timestamp if `$format` is 'U' or 'G'.
  *                          False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_the_time( $format = '', $post = null ) {
 	$post = get_post( $post );
@@ -3165,6 +3173,8 @@ function get_the_time( $format = '', $post = null ) {
  * @param bool             $translate Whether to translate the time string. Default false.
  * @return string|int|false Formatted date string or Unix timestamp if `$format` is 'U' or 'G'.
  *                          False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_post_time( $format = 'U', $gmt = false, $post = null, $translate = false ) {
 	$post = get_post( $post );
@@ -3315,6 +3325,8 @@ function the_modified_time( $format = '' ) {
  *                                 Defaults to the 'time_format' option.
  * @param int|WP_Post|null $post   Optional. Post ID or WP_Post object. Default current post.
  * @return string|int|false Formatted date string or Unix timestamp. False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_the_modified_time( $format = '', $post = null ) {
 	$post = get_post( $post );
@@ -3354,6 +3366,8 @@ function get_the_modified_time( $format = '', $post = null ) {
  * @param bool             $translate Whether to translate the time string. Default false.
  * @return string|int|false Formatted date string or Unix timestamp if `$format` is 'U' or 'G'.
  *                          False on failure.
+ *
+ * @phpstan-return ( $format is 'U'|'G' ? int|false : string|false )
  */
 function get_post_modified_time( $format = 'U', $gmt = false, $post = null, $translate = false ) {
 	$post = get_post( $post );
@@ -4944,6 +4958,12 @@ function language_attributes( $doctype = 'html' ) {
  * }
  * @return string|string[]|null String of page links or array of page links, depending on 'type' argument.
  *                              Null if total number of pages is less than 2.
+ *
+ * @phpstan-return (
+ *     $args is array{ total: int<min, 1>, ... }
+ *         ? null
+ *         : ( $args is array{ type: 'array', ... } ? list<string> : string )
+ * )
  */
 function paginate_links( $args = '' ) {
 	global $wp_query, $wp_rewrite;
diff --git a/src/wp-includes/http.php b/src/wp-includes/http.php
index c2855a8d8d9c1..1a189a261306b 100644
--- a/src/wp-includes/http.php
+++ b/src/wp-includes/http.php
@@ -555,6 +555,8 @@ function send_origin_headers() {
  *
  * @param string $url Request URL.
  * @return string|false Returns false if the URL is not safe, or the original URL if it is safe.
+ *
+ * @phpstan-return ( $url is numeric|'' ? false : string|false )
  */
 function wp_http_validate_url( $url ) {
 	if ( ! is_string( $url ) || '' === $url || is_numeric( $url ) ) {
diff --git a/src/wp-includes/l10n/class-wp-translations.php b/src/wp-includes/l10n/class-wp-translations.php
index e919fea8b94b3..2cccf542d8b3b 100644
--- a/src/wp-includes/l10n/class-wp-translations.php
+++ b/src/wp-includes/l10n/class-wp-translations.php
@@ -112,6 +112,10 @@ private function make_entry( $original, $translations ): Translation_Entry {
 	 * @param int|float   $count    Count. Should be an integer, but some plugins pass floats.
 	 * @param string|null $context  Context.
 	 * @return string|null Translation if it exists, or the unchanged singular string.
+	 *
+	 * @phpstan-template T of string|null
+	 * @phpstan-param T $singular
+	 * @phpstan-return ( $singular is null ? null : ( $plural is null ? T : string ) )
 	 */
 	public function translate_plural( $singular, $plural, $count = 1, $context = '' ) {
 		if ( null === $singular || null === $plural ) {
@@ -135,6 +139,8 @@ public function translate_plural( $singular, $plural, $count = 1, $context = ''
 	 * @param string|null $singular Singular string.
 	 * @param string|null $context  Context.
 	 * @return string|null Translation if it exists, or the unchanged singular string
+	 *
+	 * @phpstan-return ( $singular is null ? null : string )
 	 */
 	public function translate( $singular, $context = '' ) {
 		if ( null === $singular ) {
diff --git a/src/wp-includes/link-template.php b/src/wp-includes/link-template.php
index 10bda681154f9..3d4ffc23b8f62 100644
--- a/src/wp-includes/link-template.php
+++ b/src/wp-includes/link-template.php
@@ -153,6 +153,8 @@ function wp_force_plain_post_permalink( $post = null, $sample = null ) {
  * @param int|WP_Post $post      Optional. Post ID or post object. Default is the global `$post`.
  * @param bool        $leavename Optional. Whether to keep post name or page name. Default false.
  * @return string|false The permalink URL. False if the post does not exist.
+ *
+ * @phpstan-return ( $post is WP_Post ? string : string|false )
  */
 function get_the_permalink( $post = 0, $leavename = false ) {
 	return get_permalink( $post, $leavename );
@@ -166,6 +168,8 @@ function get_the_permalink( $post = 0, $leavename = false ) {
  * @param int|WP_Post $post      Optional. Post ID or post object. Default is the global `$post`.
  * @param bool        $leavename Optional. Whether to keep post name or page name. Default false.
  * @return string|false The permalink URL. False if the post does not exist.
+ *
+ * @phpstan-return ( $post is WP_Post ? string : string|false )
  */
 function get_permalink( $post = 0, $leavename = false ) {
 	$rewritecode = array(
@@ -320,6 +324,8 @@ function get_permalink( $post = 0, $leavename = false ) {
  * @param bool        $leavename Optional. Whether to keep post name. Default false.
  * @param bool        $sample    Optional. Is it a sample permalink. Default false.
  * @return string|false The post permalink URL. False if the post does not exist.
+ *
+ * @phpstan-return ( $post is WP_Post ? string : string|false )
  */
 function get_post_permalink( $post = 0, $leavename = false, $sample = false ) {
 	global $wp_rewrite;
diff --git a/src/wp-includes/load.php b/src/wp-includes/load.php
index 061754e8b4e52..1558a44189226 100644
--- a/src/wp-includes/load.php
+++ b/src/wp-includes/load.php
@@ -1832,6 +1832,8 @@ function wp_doing_cron() {
  * @return bool Whether the variable is an instance of WP_Error.
  *
  * @phpstan-assert-if-true WP_Error $thing
+ *
+ * @phpstan-return ( $thing is WP_Error ? true : false )
  */
 function is_wp_error( $thing ) {
 	$is_wp_error = ( $thing instanceof WP_Error );
diff --git a/src/wp-includes/ms-network.php b/src/wp-includes/ms-network.php
index 8ab8819e268f2..35cc6bfc06dd7 100644
--- a/src/wp-includes/ms-network.php
+++ b/src/wp-includes/ms-network.php
@@ -57,8 +57,14 @@ function get_network( $network = null ) {
  *
  * @param string|array $args Optional. Array or string of arguments. See WP_Network_Query::parse_query()
  *                           for information on accepted arguments. Default empty array.
- * @return array|int List of WP_Network objects, a list of network IDs when 'fields' is set to 'ids',
- *                   or the number of networks when 'count' is passed as a query var.
+ * @return WP_Network[]|int[]|int List of WP_Network objects, a list of network IDs when 'fields' is set
+ *                                to 'ids', or the number of networks when 'count' is passed as a query var.
+ *
+ * @phpstan-return (
+ *     $args is array{ count: true, ... } ? int : (
+ *         $args is array{ fields: 'ids', ... } ? int[] : array<int, WP_Network>
+ *     )
+ * )
  */
 function get_networks( $args = array() ) {
 	$query = new WP_Network_Query();
diff --git a/src/wp-includes/ms-site.php b/src/wp-includes/ms-site.php
index f18189c30d5a3..342058156be01 100644
--- a/src/wp-includes/ms-site.php
+++ b/src/wp-includes/ms-site.php
@@ -441,6 +441,12 @@ function update_sitemeta_cache( $site_ids ) {
  *                           for information on accepted arguments. Default empty array.
  * @return WP_Site[]|int[]|int List of WP_Site objects, a list of site IDs when 'fields' is set to 'ids',
  *                             or the number of sites when 'count' is passed as a query var.
+ *
+ * @phpstan-return (
+ *     $args is array{ count: true, ... } ? int : (
+ *         $args is array{ fields: 'ids', ... } ? int[] : array<int, WP_Site>
+ *     )
+ * )
  */
 function get_sites( $args = array() ) {
 	$query = new WP_Site_Query();
diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index aa39c31d78ce5..ff5a4d5da5621 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -97,6 +97,12 @@ function get_userdata( $user_id ) {
 	 * @param string     $field The field to retrieve the user with. id | ID | slug | email | login.
 	 * @param int|string $value A value for $field. A user ID, slug, email address, or login name.
 	 * @return WP_User|false WP_User object on success, false on failure.
+	 *
+	 * @phpstan-return (
+	 *     $field is 'id'|'ID'
+	 *         ? ( $value is int<min, 0> ? false : WP_User|false )
+	 *         : WP_User|false
+	 * )
 	 */
 	function get_user_by( $field, $value ) {
 		$userdata = WP_User::get_data_by( $field, $value );
diff --git a/src/wp-includes/plugin.php b/src/wp-includes/plugin.php
index 38e88aa96bb00..a3e9afacdb8dc 100644
--- a/src/wp-includes/plugin.php
+++ b/src/wp-includes/plugin.php
@@ -285,6 +285,13 @@ function apply_filters_ref_array( $hook_name, $args ) {
  *                  If `$callback` and `$priority` are both provided, a boolean is returned
  *                  for whether the specific function is registered at that priority.
  * @phpstan-param Maybe_Callable|false $callback
+ * @phpstan-return (
+ *     $callback is false
+ *         ? bool
+ *         : ( $priority is int
+ *             ? bool
+ *             : false|int )
+ * )
  */
 function has_filter( $hook_name, $callback = false, $priority = false ) {
 	global $wp_filter;
@@ -600,6 +607,13 @@ function do_action_ref_array( $hook_name, $args ) {
  *                  If `$callback` and `$priority` are both provided, a boolean is returned
  *                  for whether the specific function is registered at that priority.
  * @phpstan-param Maybe_Callable|false $callback
+ * @phpstan-return (
+ *     $callback is false
+ *         ? bool
+ *         : ( $priority is int
+ *             ? bool
+ *             : false|int )
+ * )
  */
 function has_action( $hook_name, $callback = false, $priority = false ) {
 	return has_filter( $hook_name, $callback, $priority );
diff --git a/src/wp-includes/rest-api.php b/src/wp-includes/rest-api.php
index c1462890213e5..5bc3c53c365c5 100644
--- a/src/wp-includes/rest-api.php
+++ b/src/wp-includes/rest-api.php
@@ -694,6 +694,8 @@ function rest_ensure_request( $request ) {
  * @return WP_REST_Response|WP_Error If response generated an error, WP_Error, if response
  *                                   is already an instance, WP_REST_Response, otherwise
  *                                   returns a new WP_REST_Response instance.
+ *
+ * @phpstan-return ( $response is WP_Error ? WP_Error : WP_REST_Response )
  */
 function rest_ensure_response( $response ) {
 	if ( is_wp_error( $response ) ) {
@@ -1531,6 +1533,8 @@ function rest_is_ip_address( $ip ) {
  *
  * @param bool|string|int $value The value being evaluated.
  * @return bool Returns the proper associated boolean value.
+ *
+ * @phpstan-return ( $value is bool ? bool : ( $value is ''|'false'|'FALSE'|'0'|0 ? false : true ) )
  */
 function rest_sanitize_boolean( $value ) {
 	// String values are translated to `true`; make sure 'false' is false.
diff --git a/src/wp-includes/revision.php b/src/wp-includes/revision.php
index 6e27fad4fa0a4..e562cd0cd5167 100644
--- a/src/wp-includes/revision.php
+++ b/src/wp-includes/revision.php
@@ -307,6 +307,12 @@ function wp_get_post_autosave( $post_id, $user_id = 0 ) {
  *
  * @param int|WP_Post $post Post ID or post object.
  * @return int|false ID of revision's parent on success, false if not a revision.
+ *
+ * @phpstan-return (
+ *     $post is WP_Post
+ *         ? false|int<0, max>
+ *         : ( $post is int<min, 0> ? false : false|int<0, max> )
+ * )
  */
 function wp_is_post_revision( $post ) {
 	$post = wp_get_post_revision( $post );
diff --git a/src/wp-includes/shortcodes.php b/src/wp-includes/shortcodes.php
index 01fed7244e548..1ba655b176733 100644
--- a/src/wp-includes/shortcodes.php
+++ b/src/wp-includes/shortcodes.php
@@ -145,6 +145,8 @@ function shortcode_exists( $tag ) {
  * @param string $content Content to search for shortcodes.
  * @param string $tag     Shortcode tag to check.
  * @return bool Whether the passed content contains the given shortcode.
+ *
+ * @phpstan-return ( $tag is empty ? false : ( $content is empty ? false : bool ) )
  */
 function has_shortcode( $content, $tag ) {
 	if ( ! str_contains( $content, '[' ) ) {
diff --git a/src/wp-includes/taxonomy.php b/src/wp-includes/taxonomy.php
index d13a11e65581c..ec24ca2ca496b 100644
--- a/src/wp-includes/taxonomy.php
+++ b/src/wp-includes/taxonomy.php
@@ -374,6 +374,8 @@ function get_taxonomy( $taxonomy ) {
  *
  * @param string $taxonomy Name of taxonomy object.
  * @return bool Whether the taxonomy exists.
+ *
+ * @phpstan-return ( $taxonomy is non-falsy-string ? bool : false )
  */
 function taxonomy_exists( $taxonomy ) {
 	global $wp_taxonomies;
@@ -979,6 +981,13 @@ function get_tax_sql( $tax_query, $primary_table, $primary_id_column ) {
  * @param string             $filter   Optional. How to sanitize term fields. Default 'raw'.
  * @return WP_Term|array|WP_Error|null WP_Term instance (or array) on success, depending on the `$output` value.
  *                                     WP_Error if `$taxonomy` does not exist. Null for miscellaneous failure.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? array<string, mixed>|WP_Error|null : (
+ *         $output is 'ARRAY_N' ? list<mixed>|WP_Error|null : WP_Term|WP_Error|null
+ *     )
+ * )
  */
 function get_term( $term, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
 	if ( empty( $term ) ) {
@@ -1101,6 +1110,13 @@ function get_term( $term, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
  * @param string     $filter   Optional. How to sanitize term fields. Default 'raw'.
  * @return WP_Term|array|false WP_Term instance (or array) on success, depending on the `$output` value.
  *                             False if `$taxonomy` does not exist or `$term` was not found.
+ *
+ * @phpstan-param 'OBJECT'|'ARRAY_A'|'ARRAY_N' $output
+ * @phpstan-return (
+ *     $output is 'ARRAY_A' ? array<string, mixed>|false : (
+ *         $output is 'ARRAY_N' ? list<mixed>|false : WP_Term|false
+ *     )
+ * )
  */
 function get_term_by( $field, $value, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
 
@@ -1822,6 +1838,14 @@ function sanitize_term( $term, $taxonomy, $context = 'display' ) {
  *                         Accepts 'raw', 'edit', 'db', 'display', 'rss',
  *                         'attribute', or 'js'.
  * @return mixed Sanitized field.
+ *
+ * @phpstan-template T of string
+ * @phpstan-param T $value
+ * @phpstan-return (
+ *     $field is 'parent'|'term_id'|'count'|'term_group'|'term_taxonomy_id'|'object_id'
+ *         ? int<0, max>
+ *         : ( $context is 'raw' ? T : ( $context is 'attribute'|'edit'|'js' ? string : mixed ) )
+ * )
  */
 function sanitize_term_field( $field, $value, $term_id, $taxonomy, $context ) {
 	$int_fields = array( 'parent', 'term_id', 'count', 'term_group', 'term_taxonomy_id', 'object_id' );
diff --git a/src/wp-includes/user.php b/src/wp-includes/user.php
index b4ab594038174..2cea28357b0d1 100644
--- a/src/wp-includes/user.php
+++ b/src/wp-includes/user.php
@@ -854,6 +854,8 @@ function delete_user_option( $user_id, $option_name, $is_global = false ) {
  *
  * @param int $user_id User ID.
  * @return WP_User|false WP_User object on success, false on failure.
+ *
+ * @phpstan-return ( $user_id is int<min, 0> ? false : WP_User|false )
  */
 function get_user( $user_id ) {
 	return get_user_by( 'id', $user_id );
@@ -869,6 +871,14 @@ function get_user( $user_id ) {
  * @param array $args Optional. Arguments to retrieve users. See WP_User_Query::prepare_query()
  *                    for more information on accepted arguments.
  * @return array List of users.
+ *
+ * @phpstan-return (
+ *     $args is array{ fields: 'all'|'all_with_meta', ... } ? array<int, WP_User> : (
+ *         $args is array{ fields: 'ID'|'id', ... } ? array<int, non-negative-int> : (
+ *             $args is array{ fields: non-empty-string|non-empty-array<array-key, string>, ... } ? array<int, mixed> : array<int, WP_User>
+ *         )
+ *     )
+ * )
  */
 function get_users( $args = array() ) {
 
diff --git a/tests/phpstan/baselines/argument.type.neon b/tests/phpstan/baselines/argument.type.neon
index 80844ad48e5ac..925f5cc743e04 100644
--- a/tests/phpstan/baselines/argument.type.neon
+++ b/tests/phpstan/baselines/argument.type.neon
@@ -729,7 +729,7 @@ parameters:
 			count: 1
 			path: ../../../src/wp-includes/class-wp-customize-manager.php
 		-
-			message: '#^Parameter \#1 \$postarr of function wp_insert_post expects array\{ID\?\: int, post_author\?\: int, post_date\?\: string, post_date_gmt\?\: string, post_content\?\: string, post_content_filtered\?\: string, post_title\?\: string, post_excerpt\?\: string, \.\.\., \.\.\.\}, array\<int\|string\|false\> given\.$#'
+			message: '#^Parameter \#1 \$postarr of function wp_insert_post expects array\{ID\?\: int, post_author\?\: int, post_date\?\: string, post_date_gmt\?\: string, post_content\?\: string, post_content_filtered\?\: string, post_title\?\: string, post_excerpt\?\: string, \.\.\., \.\.\.\}, array\<int\<min, \-1\>\|int\<1, max\>\|string\|false\> given\.$#'
 			identifier: argument.type
 			count: 1
 			path: ../../../src/wp-includes/class-wp-customize-manager.php
@@ -849,7 +849,7 @@ parameters:
 			count: 1
 			path: ../../../src/wp-includes/class-wp-widget.php
 		-
-			message: '#^Parameter \#1 \$postarr of function wp_insert_post expects array\{ID\?\: int, post_author\?\: int, post_date\?\: string, post_date_gmt\?\: string, post_content\?\: string, post_content_filtered\?\: string, post_title\?\: string, post_excerpt\?\: string, \.\.\., \.\.\.\}, array\{post_author\: int, post_date\: int\|string, post_date_gmt\: int\|string, post_content\: string, post_title\: string, post_category\: array\<string\>\|string, post_status\: ''draft''\|''publish''\} given\.$#'
+			message: '#^Parameter \#1 \$postarr of function wp_insert_post expects array\{ID\?\: int, post_author\?\: int, post_date\?\: string, post_date_gmt\?\: string, post_content\?\: string, post_content_filtered\?\: string, post_title\?\: string, post_excerpt\?\: string, \.\.\., \.\.\.\}, array\{post_author\: int, post_date\: string, post_date_gmt\: string, post_content\: string, post_title\: string, post_category\: array\<string\>\|string, post_status\: ''draft''\|''publish''\} given\.$#'
 			identifier: argument.type
 			count: 1
 			path: ../../../src/wp-includes/class-wp-xmlrpc-server.php
@@ -993,6 +993,11 @@ parameters:
 			identifier: argument.type
 			count: 2
 			path: ../../../src/wp-includes/general-template.php
+		-
+			message: '#^Parameter \#1 \$weekday_number of method WP_Locale\:\:get_weekday\(\) expects int, string\|false given\.$#'
+			identifier: argument.type
+			count: 2
+			path: ../../../src/wp-includes/general-template.php
 		-
 			message: '#^Parameter \#2 \$replace of function str_replace expects array\<string\>\|string, int\<1, max\> given\.$#'
 			identifier: argument.type
diff --git a/tests/phpstan/baselines/if.alwaysFalse.neon b/tests/phpstan/baselines/if.alwaysFalse.neon
index 6e33ed2a5365c..cc72813ceafbc 100644
--- a/tests/phpstan/baselines/if.alwaysFalse.neon
+++ b/tests/phpstan/baselines/if.alwaysFalse.neon
@@ -28,11 +28,6 @@ parameters:
 			identifier: if.alwaysFalse
 			count: 2
 			path: ../../../src/wp-includes/class-wp-block-processor.php
-		-
-			message: '#^If condition is always false\.$#'
-			identifier: if.alwaysFalse
-			count: 1
-			path: ../../../src/wp-includes/rest-api/endpoints/class-wp-rest-comments-controller.php
 		-
 			message: '#^If condition is always false\.$#'
 			identifier: if.alwaysFalse
diff --git a/tests/phpstan/baselines/isset.property.neon b/tests/phpstan/baselines/isset.property.neon
index ab7d839e22002..f5e272b598f34 100644
--- a/tests/phpstan/baselines/isset.property.neon
+++ b/tests/phpstan/baselines/isset.property.neon
@@ -186,7 +186,7 @@ parameters:
 		-
 			message: '#^Property WP_Term\:\:\$term_id \(int\) in isset\(\) is not nullable\.$#'
 			identifier: isset.property
-			count: 1
+			count: 2
 			path: ../../../src/wp-includes/nav-menu.php
 		-
 			message: '#^Property WP_Post\:\:\$post_name \(string\) in isset\(\) is not nullable\.$#'
diff --git a/tests/phpstan/baselines/property.nonObject.neon b/tests/phpstan/baselines/property.nonObject.neon
index d242b9373685b..895c9e3656d3d 100644
--- a/tests/phpstan/baselines/property.nonObject.neon
+++ b/tests/phpstan/baselines/property.nonObject.neon
@@ -183,21 +183,11 @@ parameters:
 			identifier: property.nonObject
 			count: 1
 			path: ../../../src/wp-includes/class-wp-customize-manager.php
-		-
-			message: '#^Cannot access property \$object_id on array\|WP_Error\|WP_Term\.$#'
-			identifier: property.nonObject
-			count: 1
-			path: ../../../src/wp-includes/class-wp-term-query.php
 		-
 			message: '#^Cannot access property \$term_id on string\|WP_Customize_Setting\.$#'
 			identifier: property.nonObject
 			count: 1
 			path: ../../../src/wp-includes/customize/class-wp-customize-nav-menu-control.php
-		-
-			message: '#^Cannot access property \$link_id on array\|object\.$#'
-			identifier: property.nonObject
-			count: 3
-			path: ../../../src/wp-includes/link-template.php
 		-
 			message: '#^Cannot access property \$plugins on array\|object\.$#'
 			identifier: property.nonObject
@@ -218,18 +208,8 @@ parameters:
 			identifier: property.nonObject
 			count: 1
 			path: ../../../src/wp-includes/rest-api/endpoints/class-wp-rest-plugins-controller.php
-		-
-			message: '#^Cannot access property \$parent on array\|object\.$#'
-			identifier: property.nonObject
-			count: 1
-			path: ../../../src/wp-includes/taxonomy.php
 		-
 			message: '#^Cannot access property \$template_name on array\.$#'
 			identifier: property.nonObject
 			count: 1
 			path: ../../../src/wp-includes/taxonomy.php
-		-
-			message: '#^Cannot access property \$term_id on array\|object\.$#'
-			identifier: property.nonObject
-			count: 4
-			path: ../../../src/wp-includes/taxonomy.php
diff --git a/tests/phpstan/baselines/property.notFound.neon b/tests/phpstan/baselines/property.notFound.neon
index c7d60d13061d2..460a5082ab0b8 100644
--- a/tests/phpstan/baselines/property.notFound.neon
+++ b/tests/phpstan/baselines/property.notFound.neon
@@ -293,6 +293,11 @@ parameters:
 			identifier: property.notFound
 			count: 2
 			path: ../../../src/wp-includes/class-walker-nav-menu.php
+		-
+			message: '#^Access to an undefined property WP_Error\|WP_Term\:\:\$object_id\.$#'
+			identifier: property.notFound
+			count: 1
+			path: ../../../src/wp-includes/class-wp-term-query.php
 		-
 			message: '#^Access to an undefined property WP_Query\:\:\$comments_by_type\.$#'
 			identifier: property.notFound