<?php
 
    function splitByWords($string, $start = null, $end = null) {
        $words = explode(' ', $string);
 
        $newString = '';
 
        $end = $end === null ? count($words) : $end + 1;
        $start = $start === null ? 0 : $start;
 
    	if(count($words) == 0 || count($words) < $start)
            return $string;
 
        for($i = $start; $i < $end; $i++)
            if(array_key_exists($i, $words))
                $newString .=  strlen($newString) !== 0 ? ' ' . $words[$i] : $words[$i];
 
        return $newString;
    }
 
    $string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur quis rhoncus neque. Curabitur ultrices sem luctus interdum feugiat. Sed purus nulla, rhoncus nec diam sed, sodales semper felis. Aliquam ultrices feugiat venenatis. Maecenas eu rutrum nibh, sit amet ultrices quam. Duis justo arcu, bibendum ac velit vel, cursus accumsan erat. Duis scelerisque eget augue id consectetur. Aenean bibendum sapien vel nisl imperdiet convallis. Nam a nunc justo. Etiam porttitor euismod erat, eu volutpat lacus elementum ac. Mauris scelerisque blandit eros lacinia congue. Etiam fermentum risus quis turpis semper ultricies. Phasellus lacinia, lorem eget interdum condimentum, dolor nibh euismod augue, ut euismod diam orci non nulla.";
 
    $div1 = splitByWords($string, 9, 20);
    $div2 = splitByWords($string, 80);
 
    echo $div1;
 

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