Here's a little short code I use to add some conditional magic for federating content. Use case: If the post is short, just post the content - no title; no permalink.

wp_activitypub_conditional_shortcode

<?php
function conditional_shortcode($atts, $content, $tag){
	global $post;

	$atts = shortcode_atts(
		array( 'length' => 400, 'condition' => 'gt' ),
		$atts,
		$tag
	);

	$excerpt_length = intval( $atts['length'] );

	if ( 0 === $excerpt_length ) {
		$excerpt_length = 400;
	}

	$the_content = get_the_content($post->ID);
	$content_length = strlen( $the_content );
	
	Activitypub\Shortcodes::register();
	switch($atts['condition']){
		case "lt":
			if ($content_length < $excerpt_length) {
				return do_shortcode($content);
			}
			break;
		default:
			if ($content_length >= $excerpt_length) {
				return do_shortcode($content);
			}
	}

	return '';
}
add_shortcode( 'ap_if', 'conditional_shortcode');
?>