Technically the web server always runs first. It doesn't understand PHP itself, but must be configured to detect whether the location requested by the client (browser) contains PHP segments or not. For example, any file with extension ".php" may be processed by invoking the PHP which interprets the PHP segments and feeds the entire HTML back to the server. It then returns that complete content back to the client.
here is a "server-php >> html >> browser" process illustration:
it shows the basic steps; first php code is parsed at server into html; then sent to browser, that understands html tags and renders them to the display the webpage, there's also some quick overview about the process.. worths taking a look at
before html runs to show a webpage, php code runs first on web server.
so, when there lines as follow:
echo "php runs first!";
the first step is to run php code, we get:
php runs first
then, code is sent to browser, and we see somthing~
"the code is executed on the server"
This is an important concept for the first-time PHP programmer to understand, so that when you get into string formatting later on, you understand the difference between formatting the on-screen content (as parsed by your browser) and formatting the HTML code (as returned by the server).
For example "\n" starts a new line in the HTML code, and its results are only seen if you look at the "source HTML". It is NOT the same as <br>!
[EDIT BY danbrown AT php DOT net: Corrected typo in post. Thanks to PHP at ANDY dot COM dot PT for pointing out the issue.]