Description:
------------
---
From manual page: http://www.php.net/function.strip-tags#refsect1-function.strip-
tags-parameters
---
the note says that the second parameter allowable_tags "sees a tag as a case-
insensitive string between < and the first whitespace or >."

But it gives a wrong example,because strip_tags("<br/>", "<br>") return a 
string.just see the test script.

And the right example should be like below script:
$tt=strip_tags("<br/>","<br >");//just give the second prarameter a whitespace

var_dump($tt);//which returns string(0)""

Test script:
---------------
$test=strip_tags("<br/>","<br>");

var_dump($test);//which returns string(5)""


$tt=strip_tags("<br/>","<br >");//just give the second prarameter a whitespace

var_dump($tt);//which returns string(0)""