Length of the General Comment

Hi!

You're trying to access the variable $semantic_field that doesn't exist. You get $semantics which is an object that holds all the fields. You'll have to parse it to get to the correct field first. That's what the foreach loop in https://h5p.org/comment/18767#comment-18767 is doing (for one level of the object tree).

Best,
Oliver

function h5pmods_alter_semantics( &$semantics, $library_name ) {
  if ( $library_name === 'H5P.MultiChoice' ) {

    foreach ( $semantics as $semantic_field ) {
      if ( $semantic_field->name === 'overallFeedback' ) {
        $semantic_field->label = 'Final feedback (this is a test)';

        $overall_feedback_fields = $semantic_field->fields;
        foreach( $overall_feedback_fields as $overall_feedback_field ) {

          if ( $overall_feedback_field->name === 'overallFeedback' ) {
              $overall_feedback_field->label = 'This is another test';
          }

          // Won't work, see explanation below
          if ( $overall_feedback_field->name === 'feedback' ) {
              $overall_feedback_field->label = 'Gran retroalimentación';
          }

          /*
           * The part of the editor's semantics that $overall_feedback_fields is
           * holding is https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L160-L210
           * It contains just one element ("name": "overallFeedback") that you
           * can see at
           * https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L161-L209
           * There's none that's named "feedback", so that cannot be found.
           * We need to dig deeper.
           * You can see that the overallFeedback field has other properties
           * next to name: type (list), importance (high), ... , AND "field".
           * https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L177-L208
           * So we would have to look at $overall_feedback_field->field that one is
           * also named "overallFeedback", so not the one you are looking for.
           * But that group has a property fields that contains three elements:
           * https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L181-L206
           * One of them is the one you are looking for. So, let's just loop
           * over $overall_feedback_field->field->fields until we find the one
           * that you want to change ...
           */
          $overall_feedback_elements = $overall_feedback_field->field->fields;
          foreach( $overall_feedback_elements as $overall_feedback_element ) {
            if ( $overall_feedback_element->name === 'feedback' ) {
              $overall_feedback_element->maxLength = 1000;
            }
          }
        }
      }
    }
  }
}
add_action( 'h5p_alter_library_semantics', 'h5pmods_alter_semantics', 10, 4 );

My bad. My example wasn't properly nested ...

function h5pmods_alter_semantics( &$semantics, $library_name ) {
  if ( $library_name === 'H5P.MultiChoice' ) {

    foreach ( $semantics as $semantic_field ) {
      if ( $semantic_field->name === 'overallFeedback' ) {
        // We're now at "overallFeedback"
        // https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L155

        $semantic_field->label = 'Final feedback (this is a test)';

        $overall_feedback_fields = $semantic_field->fields;
        foreach( $overall_feedback_fields as $overall_feedback_field ) {

          if ( $overall_feedback_field->name === 'overallFeedback' ) {
            // We're now at "overallFeedback/overallFeedback"
            // https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L162

            $overall_feedback_elements = $overall_feedback_field->field->fields;
            foreach( $overall_feedback_elements as $overall_feedback_element ) {

              if ( $overall_feedback_element->name === 'feedback' ) {
                // We're now at "overallFeedback/overallFeedback/overallFeedback/feedback"
                // https://github.com/h5p/h5p-multi-choice/blob/master/semantics.json#L200

                $overall_feedback_element->placeholder = 'I can not take up to 1000 chars!';
                $overall_feedback_element->maxLength = 1000;
              }
            }
          }
        }
      }
    }
  }
}

You're welcome! And kudos to you for your perseverance! Most people wouldn't even have started ("oh, that's coding, I can't do this").