Decoding WordPress PHP: Why Do We Use if ( … ) : Instead of {}?

As I dive deeper into the world of WordPress Full Site Editing (FSE) theme development, I’m spending a lot of time dissecting the default Block Themes—like Twenty Twenty-Five.

FSE is shifting so much of theme development into theme.json and block markup, but PHP remains the backbone of how our themes actually function. Recently, while looking at the functions.php file in a default theme, I stumbled upon a piece of syntax that always used to confuse me:

if ( ! function_exists( 'my_theme_setup' ) ) :
    // ... function code here ...
endif;

Wait a second. Where are the curly braces {}? Why is there a colon : after the if statement?

If you’ve ever asked yourself the same questions, you aren’t alone. Today, I want to break down this quirky PHP syntax, explain why WordPress loves it, and discuss whether you should be using it in your own FSE themes.

The Alternative Syntax Explained

That colon is part of PHP’s alternative syntax for control structures. It does the exact same thing as the standard curly-brace syntax; it’s just a different way of writing it.

Here is a side-by-side comparison:

The Standard Way:

if ( ! function_exists( 'my_theme_setup' ) ) {
    function my_theme_setup() {
        // Setup code
    }
}

The Alternative Way:

if ( ! function_exists( 'my_theme_setup' ) ) :
    function my_theme_setup() {
        // Setup code
    }
endif;

Functionally, these are identical. PHP doesn’t care which one you use. But if they do the same thing, why does WordPress consistently use the colon method?

The “Why”: Readability in the Trenches

The primary reason for the alternative syntax is readability when mixing PHP and HTML.

As theme developers, we are constantly jumping in and out of PHP to output HTML. When you have nested if statements, foreach loops, and while loops all mixed with HTML, a wall of closing curly braces } becomes a nightmare to read. You find yourself scrolling up and down asking, “Which } closes the if statement, and which closes the loop?”

The alternative syntax solves this by explicitly labeling the closing tag. Consider this classic loop example:

Using Curly Braces (Hard to read):

<?php if ( have_posts() ) { ?>
    <div class="post-list">
        <?php while ( have_posts() ) { 
            the_post(); ?>
            <h2><?php the_title(); ?></h2>
        <?php } ?>
    </div>
<?php } ?>

Look at the bottom. You have } and }. It’s not immediately obvious what belongs to what.

Using the Colon Syntax (Much clearer):

<?php if ( have_posts() ) : ?>
    <div class="post-list">
        <?php while ( have_posts() ) : 
            the_post(); ?>
            <h2><?php the_title(); ?></h2>
        <?php endwhile; ?>
    </div>
<?php endif; ?>

Now, the bottom is perfectly clear: endwhile; closes the loop, and endif; closes the condition. It’s a breath of fresh air for readability.

Why use it in functions.php?

You might be thinking: “Okay, I get it for HTML templates. But the code snippet I showed at the beginning was from functions.php, which is pure PHP! Why use it there?”

You caught me! In pure PHP files, the readability benefit of mixing HTML doesn’t apply. However, in WordPress, using the colon syntax for pluggable functions has become a cultural convention.

The if ( ! function_exists() ) : pattern is how WordPress creates “pluggable” functions. It allows a child theme to define the same function, effectively overriding the parent theme. Because this is such a vital concept in WordPress theme development, using endif; acts as a visual “bookend.” When you are scrolling through hundreds of lines of code in functions.php and see endif;, you instantly know: “Ah, this is the end of a pluggable function override check.”

Is it Best Practice for FSE Theme Developers?

This is where nuance comes in. The short answer is: It depends on the file.

• In PHP Template Files / Block Render Callbacks: YES. Even in FSE, you will write PHP to render dynamic blocks or create custom block patterns via PHP. Whenever you are mixing PHP logic and HTML output, using if : ... endif; and while : ... endwhile; is a WordPress best practice. It is explicitly recommended in the WordPress Coding Standards.
• In Pure Logic Files (functions.php, Classes): IT’S UP TO YOU. General PHP standards (like PSR-12) actually prefer curly braces {} for pure logic files. However, because WordPress has its own long-standing conventions, you will see the colon syntax used frequently even in functions.php. Neither is “wrong” here.

The Takeaway

As FSE theme developers, we are navigating the bridge between classic WordPress PHP conventions and modern block-based development. While theme.json handles most of the visual setup now, understanding why WordPress code looks the way it does empowers us to write cleaner, more maintainable PHP for our dynamic blocks and theme setups.

The next time you see that colon : in a theme file, you don’t need to be confused. You can just smile, knowing it’s there to make your life a little easier when you’re deep in the code.

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Are you building FSE themes? What PHP quirks have you run into lately? Let’s chat in the comments below!