HtmlHelper

<?php

final class HtmlBuilder {

    private $_elements = array();

    public function addElement(HtmlElement $element) {
        if ($element == null)
            return;
        $this->_elements[] = $element;
    }

    public function render() {
        foreach ($this->_elements as $element) {
            echo $element->render();
        }
    }

}

abstract class HtmlElement {

    protected $commonAttributes = array("id", "class", "title");
    protected $customAttributes = array();
    protected $attributes;
    protected $output;

    protected function __construct() {
        $this->attributes = new AttributeCollection();
        $this->output = "";
    }

    public function setAttribute(Attribute $attribute) {
        if ($this->isValidAttribute($attribute->name)) {
            $this->attributes->addAttribute($attribute);
        }
    }

    protected function isValidAttribute($name) {
        if (in_array($name, $this->commonAttributes) || in_array($name, $this->customAttributes))
            return true;
        return false;
    }

    public abstract function render();
}

final class Attribute {

    public $name;
    public $value;

    public function __construct($name, $value) {
        $this->name = $name;
        $this->value = $value;
    }

}

final class AttributeCollection {

    private $_attributes = array();

    public function addAttribute(Attribute $attribute) {
        if ($attribute == null)
            return;
        $this->_attributes[] = $attribute;
    }

    public function attributeExists($name) {
        foreach ($this->_attributes as $attribute) {
            if ($attribute->name == $name)
                return true;
        }
        return false;
    }

    public function getValue($name) {
        if ($this->attributeExists($name)) {
            foreach ($this->_attributes as $attribute) {
                if ($attribute->name == $name) {
                    return $attribute->value;
                }
            }
        }
    }

    public function getAttributes() {
        return $this->_attributes;
    }

}

final class Image extends HtmlElement {

    public function __construct() {
        parent::__construct();
        $this->customAttributes = array("src", "alt", "height", "width");
    }

    public function render() {
        $this->output .= "<img";
        foreach ($this->attributes->getAttributes() as $attribute) {
            $this->output .= ' ' . $attribute->name . '="' . $attribute->value . '"';
        }
        $this->output .= ' />';
        return $this->output;
    }

}