main/lib/response.php

См. документацию.

<?php
namespace Bitrix\Main;
 
abstract class Response
{
    /** @var string */
    protected $content;
 
    public function __construct()
    {
    }
 
    public function clear()
    {
    }
 
    public function flush($text = '')
    {
        $this->writeBody($text);
    }
 
    /**
     * Sets content.
     * Valid types are strings, numbers, null, and objects that implement a __toString() method.
     *
     * @param mixed $content Content that can be cast to string.
     *
     * @return $this
     * @throws ArgumentTypeException
     */
    public function setContent($content)
    {
        if (!$this->checkContent($content))
        {
            throw new ArgumentTypeException('content', 'string');
        }
 
        $this->content = (string)$content;
 
        return $this;
    }
 
    /**
     * Appends content.
     * Valid types are strings, numbers, null, and objects that implement a __toString() method.
     *
     * @param mixed $content Content that can be cast to string.
     *
     * @return $this
     * @throws ArgumentTypeException
     */
    public function appendContent($content)
    {
        if (!$this->checkContent($content))
        {
            throw new ArgumentTypeException('content', 'string');
        }
 
        $this->content .= (string)$content;
 
        return $this;
    }
 
    protected function checkContent($content)
    {
        return (
            $content === null ||
            is_string($content) ||
            is_numeric($content) ||
            is_callable(array($content, '__toString'))
        );
    }
 
    /**
     * Returns content of response.
     *
     * @return string
     */
    public function getContent()
    {
        return $this->content;
    }
 
    /**
     * Sends content to the output.
     *
     * @return void
     */
    public function send()
    {
        $this->flush($this->content);
    }
 
    protected function writeBody($text)
    {
        echo $text;
    }
}