$new_text = preg_replace('#^(.*){20}#','replace',$text);
<? echo $content->parent_id."__".$сhildren[$i]->id_content; if($content->parent_id == $children[$i]->id_content) { ?> _1<div style="display:block;"> <? } else { ?> _2<div style="display:none;"> <? } ?>
<?php echo $content->parent_id."__".$сhildren[$i]->id_content; if($content->parent_id == $children[$i]->id_content) {echo "_1<div style=\"display:block;\">";} else { echo "_2<div style=\"display:none;\"> } ?>
if($content->parent_id == $сhildren[$i]->id_content) echo '<div style="display:block;">'; else echo '<div style="display:none;">';
echo $content->parent_id == $сhildren->id_content ? '<div style="display:block;">' : '<div style="display:none;">';