What's the difference between <?php ?> and <?= ?>

<?php  ?> is a regular php opening and closing tag

<?=  ?> is a short hand for <?php  echo  '' ;  ?> 

<?php

$s="hello world";

?>

<span ><?= $s ?></span>

<br>

<?php

$s="hello world";

?>

<span ><?php echo $s ?></span>

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The Results is:

     hello world 

     hello world

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If this is what you mean....

<?php

// Mostly used way and Correct way of coding

?>

<?

// To use this tags we have to make change in php.ini file. we need to enable short_open_tag

?>

both are tabs and used for php code no difference in both statements.