example.php

<?php
/**
 * My Plugin
 * 
 * @uses add_filter() for 'the_content': make love not content
 * @uses add_filter() for 'get_the_excerpt': clearly announce all excerpts
 */
class my_plugin
{
	function __construct() {
		// make love not content
		add_filter( 'the_content', function ( $content ) {
			return $content . " ♥";
		});
		
		// clearly announce all excerpts
		add_filter( 'get_the_excerpt', function ( $excerpt ) {
			return '<strong>' . __( 'EXCERPT' ) . ':</strong> ' . $excerpt;
		});
	}
}

status-quo.php

<?php
add_filter( 'tag', 'myfunname' /* ... */ );
add_filter( 'tag', array( $this, 'myfunname' )  /* ... */ );
add_filter( 'tag', array( __CLASS__, 'myfunname' )  /* ... */ );