A PHP script can be placed anywhere in the document.
A PHP script starts with `<?php` and ends with `?>`
Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page
````<!DOCTYPE html>
<html>
<body>
<h1>My first PHP page</h1>
<?php echo "Hello World!"; ?>
</body>
</html>
````
The output of that would be :
````
My first PHP page
Hello World!
````
#### Note: PHP statements end with a semicolon (;).
# Comments in PHP
PHP supports several ways of commenting:
````
<!DOCTYPE html>
<html>
<body>
<?php
// This is a single-line comment
# This is also a single-line comment
/*
This is a multiple-lines comment block
that spans over multiple
lines
*/
// You can also use comments to leave out parts of a code line
$x = 5 /* + 15 */ + 5;
echo $x;
?>
</body>
</html>
````
# PHP Case Sensitivity
In PHP, all keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are NOT case-sensitive.
### However; all variable names are case-sensitive.
In the example below, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are treated as three different variables):