正则去掉空格

Question

<?php
$str = <<<str
<div id="new1"> <div id="new2">  <h3>   我是文字  </h3>  <span></span> </div> </div>  
str;
preg_match_all("|.*(?=<[^>]+>)|iU",$str,$match);
print_r($match);
?> 
目标是去掉各标签之间的空格，比方
<div id="new1"> <div id="new2"> -> <div id="new1"><div id="new2">
<h3>   我是文字  </h3>  -> <h3>我是文字</h3>

Answer 1

echo preg_replace("/>\s+</", '><', $str);

Answer 2

echo preg_replace("/>\s*([^\s]+)\s*</", '>\\1<', $str);

Answer 3

<?php
$str = <<<str
<div id="new1"> <div id="new2">  <h3>   我是文字  </h3>  <span></span> </div> </div>  
str;
echo preg_replace("/(?<=>)\s+|\s+(?=<)/", '', $str);
?>