Description:
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Query String doesn't bring the value after #. The string after #(including #) are ignored 

Example:

If I give an URL like: http://www.example.com/index.html#tab1 in the browser

I am trying to make up a page with tabs in which the following should happen: 

If given http://www.example.com/index.html#tab1, this should enable the tab1 by default (while loading the page). I am handling this in PHP, JS

if given http://www.example.com/index.html#tab2, this should enable the tab2 by default (while loading the page). I am handling this in PHP, JS

in JS when I give window.location, it gives all the string after # too, but this is not happening in PHP

Reproduce code:
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<?PHP
//assuming browser has opened the url: http://www.example.com/index.html#tab1
echo $_SESSION[ 'QUERY_STRING' ];
?>

Expected result:
----------------
#tab1

Actual result:
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NULL value