The are two scenarios for using shortcodes:

• The shortcode is a self-closing tag like we seen in the Basic Shortcodes section.
• The shortcode is enclosing content.

Enclosing Content

Enclosing content with a shortcode allows manipulations on the enclosed content.

[wporg]content to manipulate[/wporg]

As seen above, all you need to do in order to enclose a section of content is add a beginning [$tag] and an end [/$tag], similar to HTML.

Processing Enclosed Content

Lets get back to our original [wporg] shortcode code:

function wporg_shortcode( $atts = array(), $content = null ) {
    // do something to $content
    // always return
    return $content;
}
add_shortcode( 'wporg', 'wporg_shortcode' );

Looking at the callback function we see that we chose to accept two parameters, $atts and $content. The $content parameter is going to hold our enclosed content. We will talk about $atts later.

The default value of $content is set to null so we can differentiate between a self-closing tag and enclosing tags by using PHP function is_null().

The shortcode [$tag], including its content and the end [/$tag] will be replaced with the return value of the handler function.

Shortcode-ception

The shortcode parser performs a single pass on the content of the post.

This means that if the $content parameter of a shortcode handler contains another shortcode, it won’t be parsed. In this example, [shortcode] will not be processed:

[wporg]another [shortcode] is included[/wporg]

Using shortcodes inside other shortcodes is possible by calling do_shortcode() on the final return value of the handler function.

<pre class="wp-block-syntaxhighlighter-code">function wporg_shortcode( $atts = array(), $content = null ) {
	// do something to $content
	// run shortcode parser recursively
	$content = do_shortcode( $content );
	// always return
	return $content;
}
add_shortcode( 'wporg', 'wporg_shortcode' );</pre>

Limitations

The shortcode parser is unable to handle mixing of enclosing and non-enclosing forms of the same [$tag].

[wporg] non-enclosed content [wporg]enclosed content[/wporg]

Instead of being treated as two shortcodes separated by the text “non-enclosed content“, the parser treats this as a single shortcode enclosing “non-enclosed content [wporg]enclosed content“.