code: function receiveIframeMessage(event) {
      const data = uiFns.receiveIframeMessageBoilerplate(event);
  
      if (!data) {
        return;
      }
  
      if (data.codeOverlay) {
        if (data.codeOverlay === 'on') {
          // Can assume we're not viewing the Mustache Browser.
          codeViewer.mustacheBrowser = false;
  
          // Make sure the annotations overlay is off before showing code view.
          window.annotationsViewer.annotationsActive = false;
  
          uiProps.sgTAnnotations.classList.remove('active');
          window.annotationsViewer.slideAnnotations($sgCodeContainer.outerHeight());
  
          // Make codeViewer and nav reflect that code view is active.
          codeViewer.codeActive = true;
          codeViewer.viewall = data.viewall || false;
          uiProps.sgTCode.classList.add('active');
  
          // Update code.
          codeViewer.updateCode(data.lineage, data.lineageR, data.patternPartial, data.patternState);
        }
        else {
          codeViewer.closeCode();
        }
      }
      else if (typeof data.codeMustacheBrowser === 'boolean') {
        codeViewer.mustacheBrowser = data.codeMustacheBrowser;
      }
      else if (typeof data.codeViewall === 'boolean') {
        codeViewer.viewall = data.codeViewall;
      }
  
      switch (data.event) {
        case 'patternlab.keyPress':
          switch (data.keyPress) {
            case 'ctrl+shift+c':
              codeViewer.toggleCode();
  
              break;
  
            case 'ctrl+alt+m':
            case 'ctrl+shift+u':
              codeViewer.swapCode('m');
  
              break;
  
            case 'ctrl+alt+h':
            case 'ctrl+shift+y':
              codeViewer.swapCode('e');
  
              break;
  
            case 'mod+a':
              codeViewer.selectCode();
  
              break;
  
            case 'esc':
              if (codeViewer.codeActive) {
                codeViewer.closeCode();
              }
  
              break;
          }
  
          break;
      }
    }
docs: This gets attached as an event listener, so do not use arrow function notation.
  
  @param {object} event - Event object.