diff --git a/src/MD_STD_IN.php b/src/MD_STD_IN.php
index 16b08b5..a5bff94 100644
--- a/src/MD_STD_IN.php
+++ b/src/MD_STD_IN.php
@@ -14,7 +14,7 @@ final class MD_STD_IN {
      *
      * @param mixed $input Input string.
      *
-     * @return integer
+     * @return positive-int
      */
     public static function sanitize_id(mixed $input):int {
 
@@ -39,7 +39,7 @@ final class MD_STD_IN {
      *
      * @param mixed $input Input string.
      *
-     * @return integer
+     * @return 0|positive-int
      */
     public static function sanitize_id_or_zero(mixed $input):int {
 
@@ -92,7 +92,7 @@ final class MD_STD_IN {
      *
      * @param mixed $input Input string.
      *
-     * @return string
+     * @return non-empty-string
      */
     public static function sanitize_rgb_color(mixed $input):string {
 
@@ -117,7 +117,7 @@ final class MD_STD_IN {
      *
      * @param array<mixed> $inputs Input array.
      *
-     * @return list<integer>
+     * @return list<positive-int>
      */
     public static function sanitize_id_array(array $inputs):array {