docs: function onContentChanged( contentStringOrObject ) {
      try {
          const
              isString = typeof contentStringOrObject === 'string',
              content = isString ? Icons.iconsBook[ contentStringOrObject ] : contentStringOrObject;
  
          this._content = createSvgFromDefinition.call( this, content );
          if ( !this._content ) return;
          $.clear( this, this._content.svgRootGroup );
  
          // Update pens' colors.
          for ( const penIndex of [ 0, 1, 2, 3, 4, 5, 6, 7 ] ) {
              updatePen.call( this, penIndex, this[ `pen${penIndex}` ] );
          }
  
          this.$.style.display = "";
      } catch ( ex ) {
          this.$.style.display = "none";
          if ( this.content !== '' ) this.content = '';
      }
  }