@@// In a theme, plugin, or whatever. This filter controls an <h2> with the text "Title".

<div class="foobar">
	<h2><?php echo apply_filters( 'coolprefix_some_random_title', 'Title' ); ?></h2>

<?php
	// By default, the content is not shown. We can change this filter to "true" to show it.
	if ( true == apply_filters( 'coolprefix_displaycontent', false ) :
?>
	<p>Some content.</p>
<?php endif; ?>
</div>


@@// In a plugin or the theme's functions.php file.

<?php

add_filter( 'coolprefix_some_random_title', 'my_title_function' );
add_filter( 'coolprefix_displaycontent', 'my_content_function' );

function my_title_function( $title ) {
	// Add something onto the end of the existing title
	$title = $title . ' Is Cool';

	// Or ignore any existing data (from other filters or the theme)
	$title = 'New Title';

	// This is important as we need to allow other filters to filter what we return
	// And to allow the usage of the filter in PHP (i.e. storing it to a variable)
	return $title;
}

// This function doesn't accept any parameters because we don't care what was passed to it (i.e. the existing value)
function my_content_function() {
	return true;
}

?>