content_tag function in PHP to work as Rails content_tag function

content-tag.php

<?php

/**
 * @param $tag
 *
 * @return string
 */
function close_tag($tag)
{
    return "</" . $tag . ">";
}

/**
 * @param array $attr
 *
 * @return null|string
 */
function generate_attr_string($attr = array())
{
    $attr_string = null;
    if ( ! empty($attr)) {
        foreach ($attr as $key => $value) {
            // If we have attributes, loop through the key/value pairs passed in
            //and return result HTML as a string

            // Don't put a space after the last value
            if ($value == end($attr)) {
                $attr_string .= $key . "=" . '"' . $value . '"';
            } else {
                $attr_string .= $key . "=" . '"' . $value . '" ';
            }
        }
    }

    return $attr_string;
}

/**
 * @param $tag
 * @param array $attr
 *
 * @return string
 */
function open_tag($tag, $attr = array())
{
    $attr_string = generate_attr_string($attr);

    return "<" . $tag . " " . $attr_string . ">";
}

/**
 * Create a dynamic html tag
 *
 * @see http://andrewberls.com/blog/post/formatting-dynamic-html-tags-in-php
 *
 * @param string $tagName
 * @param string $content
 * @param array $attr
 *
 * @example content_tag("h1", "Hello", array("class" => "title"));
 *
 * @return string
 */
function content_tag($tagName = "h2", $content = "", $attr = array())
{
    return open_tag($tagName, $attr) . $content . close_tag($tagName);
}