PHP string class

The class will contain functions for multiple operations related to strings.

<?php
/**
* This class handles all kings of string processing.
* @package Sami's strings class 
* @version $Id: samis_strings.php v.1.0 2018-02-01 13:41:00 $
* @author Samuil Banti
* @copyright (C) 2018 - Samuil Banti
* @license GNU/GPLv3 http://www.gnu.org/licenses/gpl-3.0.html
*/
class samis_strings {

    /**
    * Escapes the HTML entities of specific tag content.
    * Useful for code formating.
    * @param string $string - The string to escape.
    * @param string $tag - The tag to convert
    * @return string - The string with escaped tags content.
    */
    public function escape_tag_content($string, $tag = 'pre') 
    {
	if(preg_match_all("'<{$tag}(.*?)>(.*?)<\/{$tag}>'si", $string, $matches)) {
	    $escaped_content = array();
	    foreach($matches[2] as $k => $match) {
		$escaped_content = str_replace($match, htmlentities($match), $matches[0][$k]);
		$string = str_replace($matches[0][$k], $escaped_content, $string);
	    }
	}
	return $string;
    }

    /**
    * Converts the URLs in a string into clickable links if they are not.
    * @param string $string - The string with the URLs.
    * @param string $href_tags - The tags to be added to the links.
    * @return string - The string with the clickable links.
    */
    public function urls_to_links($string, $href_tags = 'target="_blank"') {       
	$regex = "/[^\"'](http|https)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,6}(\/\S*)+?/";
	if(preg_match($regex, $string, $matches)) {
	    $url = trim($matches[0], PHP_EOL);
	    return preg_replace($regex, '<a href="'.$url.'" '.$href_tags.'>'.$url.'</a> ', $string);
	} 
	return $string;
    }

    /**
    * Get the number of frequencies of each word in a text.
    * NOTE: If the text contains tags they will be removed.
    * @param string $text - The text that will be analysed.
    * @return array - Array with words and the number of occurrences.
    */
    function words_frequency($text)
    {
	$text = str_replace([PHP_EOL,'<'], [' ',' <'], $text);
	$text = strip_tags($text);
	$text = preg_replace('/[-?.!,{}()|;=+]/', '', $text);
	$words_frequency = array();
	$text = explode(' ', $text);
	foreach($text as $v) {
	    $v = trim($v);
	    if(empty($v)) {
		continue;
	    }
	    $v = mb_strtolower($v, 'utf-8');
	    if(array_key_exists($v, $words_frequency)) {
		++$words_frequency[$v];
	    } else {
		$words_frequency[$v] = 1;
	    }
	}
	arsort($words_frequency);
	return $words_frequency;
    }

}

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