src/Sender/Builder/Http20Builder.php
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 $this;
    }
public function addDefaultVisitors(): Http20Builder
    {
        if ($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;
    }
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.