That subject statement is true, and if you want to understand how websites work, here’s the most fundamental thing you can learn: Web pages exist like ghosts, only in your web-broswer. When you visit a website, it is not like seeing a painting  thru a window. The webpage itself does not exists in finished form on the server.

What the server does is send build instructions to your browser, just like your Ikea shelving comes with an instruction sheet o how to assemble the parts. It is your own personal copy of your web-browser that actually assembles the page for you to see.

You can see this in action on most sites by simply resizing your browser window, and watching the layout change. If you access a site on the small screen of your iPhone, it  looks entirely different than if you are using a big monitor.

———-  the longer version:

As you learn about websites, there’s one fundamental thing that may lift some (if any) fog.

Servers and their websites do NOT serve up finished web pages; they send -instructions- on how to build the page in each user’s web browser. ALL the assembly work to create a page for the user to view is done on each individual user’s computer, not on the server.

Web browsers are not passive; they are actual machines, which follow the HTML/PHP/CCS/JS instructions given to them, and build each page independently, according to those instructions. As you can imagine, it’s much faster to serve up instructions than it is to serve up a finished page. That speed advantage is why websites all work this way.

Each browser (Netscape, Safari, Firefox and so on) has its own engine (that’s actually what it’s called) for building pages, and each engine is slightly different from the other. The publishers think those differences are “features” but what it really means is that to use some unique “feature” you’d have to write instructions specifically for that one browser. The down side is that also results in pages that will not render correctly on other (competitor) browsers.

That’s why when you hear geeks ask “what browser are you using?” – it’s not because one is prettier than another, but because the rendering engine is different.

In fact, in the old days, before there was any standardization of the languages, we would have to do literally that: write HTML code that checked what browser was running and jumped to special code just for that browser:
if [browser == “netscape”] then set color $FF0000;
else
if [browser == “safari”] then set color ‘red’;
else
if…..

It was numbingly tedious and completely ridiculous, and yes: it was a nightmare. Eventually however a standards body was formed, and while it took over a decade, things finally homogenized (for the most part.)

Today, for maximum compatibility, WordPress uses only standards-compliant code, and when you hit “Preview” in WordPress to see your latest changes, WordPress is really just running a built-in generic browser and sending your instructions to it.

(Yes, that means it’s quite possible that what you see in Preview Mode will not exactly match what you see once the page is published (although the differences will likely be difficult to notice, fortunately.)

So: a browser isn’t looking thru a window at a page on our site; nor is the site sending a finished page back, all neatly laid out like a PDF. Instead, websites send out Ikea-like assembly sheets, and leave it to each user’s current browser to assemble the final page for viewing.

Just thought you’d like to know.