Improved message presented to user

h5p.classes.php

@@ -3132,7 +3132,30 @@ class H5PContentValidator {
       return;
     }
     if (!in_array($value->library, $semantics->options)) {
-      $this->h5pF->setErrorMessage($this->h5pF->t('Library used in content is not a valid library according to semantics'));
+      $message = NULL;
+      // Create an understandable error message:
+      $machineName = explode(' ', $value->library)[0];
+      foreach ($semantics->options as $semanticsLibrary) {
+        $semanticsMachineName = explode(' ', $semanticsLibrary)[0];
+        if ($machineName === $semanticsMachineName) {
+          // Using the wrong version of the library in the content
+          $message = $this->h5pF->t('The version of the H5P library %machineName used in this content is not valid. Content contains %contentLibrary, but it should be %semanticsLibrary.', array(
+            '%machineName' => $machineName,
+            '%contentLibrary' => $value->library,
+            '%semanticsLibrary' => $semanticsLibrary
+          ));
+          break;
+        }
+      }
+
+      // Using a library in content that is not present at all in semantics
+      if ($message === NULL) {
+        $message = $this->h5pF->t('The H5P library %library used in the content is not valid', array(
+          '%library' => $value->library
+        ));
+      }
+
+      $this->h5pF->setErrorMessage($message);
       $value = NULL;
       return;
     }