PHP, Javascript, CSS block scripting

How can server, browser or we can recognise what kind of script at an HTML document? We use some block scripting to open and end it up.
For PHP we use

<?php

php script goes here
?>
we can also use this:

<?

php script goes here

?>

but I always use <?php and ?>

For Javascript we use

<script type="text/javascript">

Javascript script goes here

</script>

we can also use this

<script>

Javascript script goes here

</script>

For CSS we use

<style type="text/css">

CSS style goes here
</style>