// First remove the leading/trailing whitespace
//去掉开始和结束的空白
$str = trim($str);

// Now remove any doubled-up whitespace
//去掉跟随别的挤在一块的空白
$str = preg_replace('/s(?=s)/','',$str);

// Finally,replace any non-space whitespace,with a space
//最后，去掉非space 的空白，用一个空格代替
$str = pregreplace('/[nrt]/',' ',$str);
// Echo out: 'This line contains liberal use of whitespace.'
echo "

{$str}