Inserting widgets within the_content

I’m inquiring about inserting code within the the_content in my template’s single.php file.

add it inside your template’s functions.php.

<?php // example
function my_single_content_filter($content)
{ global $wp_query;

	if (!$wp_query->is_single) return $content;

	$output = PHP_EOL;
	$output .= '<div style="float:right;width:210px">';
	$output .= '<h3>random</h3>';
	$output .= '<p>Thanks for all the fish.</p>';
        $output .= '<p><a href="#">links</a> ... </p>';
	$output .= '</div>';

	return $output.$content;
}

add_action('the_content','my_single_content_filter');
?>

Is it possible to put PHP in the output? I keep getting parse errors when I try…