WordPress Spoiler BBCode

functions.php

<?php

// Thanks to the WordPress Shortcode API it is super easy to implement BBCodes for WordPress sites
// Usage: [SPOILER]Lorem ipsum...[/SPOILER], [SPOILER title="Optional title"]Lorem ipsum...[/SPOILER]
// Make it beautiful with your custom css for .spoiler :)

// The following snippet goes into the functions.php of your theme or child-theme.

add_shortcode( 'SPOILER', 'bb_code_spoiler' );

function bb_code_spoiler( $atts, $content = null ) {
  
	$a = shortcode_atts( array(
		'title' => '',
	), $atts );

	$output = '<details class="spoiler"><summary>%s</summary>%s</details>';

	return sprintf(
		$output,
		'' !== $a['title'] ? 'Spoiler: ' . $a['title'] : 'Spoiler',
		wpautop( $content )
	);

}