WordPress at a glance
filter is not described

the_meta_key filter-hook . WP 2.2.0

Filters the HTML output of the li element in the post custom fields list.

Usage

add_filter( 'the_meta_key', 'filter_function_name_8426', 10, 3 );
function filter_function_name_8426( $html, $key, $value ){
	// filter...

	return $html;
}
$html(string)
The HTML output for the li element.
$key(string)
Meta key.
$value(string)
Meta value.

Where the hook is called

the_meta()
wp-includes/post-template.php 1052
echo apply_filters( 'the_meta_key', $html, $key, $value );

Where the hook is used (in WP core)

Does not used.