code: public function addDefaultVisitors(): Http20Builder
      {
          if ($this->addedDefaultVisitors) {
              return $this;
          }
  
          $this->addedDefaultVisitors = true;
  
          $this->addVisitor(new AddExpirationHeaderVisitor());
          $this->addVisitor(new AddPriorityHeaderVisitor());
          $this->addVisitor(new AddApnIdHeaderVisitor());
          $this->addVisitor(new AddCollapseIdHeaderVisitor());
  
          return $this;
      }
docs: Add default visitors
  
  @return Http20Builder
  
  @deprecated This method is deprecated and will be a move to private scope.
  Please do not use this method in your code.
  This method will be called from the constructor of this builder.