WordPress at a glance
action is not described

pre_get_comments action-hook . WP 3.1.0

Fires before comments are retrieved.

Usage

add_action( 'pre_get_comments', 'action_function_name_6054' );
function action_function_name_6054( $this ){
	// action...
}
$this(WP_Comment_Query)
Current instance of WP_Comment_Query (passed by reference).

Where the hook is called

WP_Comment_Query::get_comments()
pre_get_comments
wp-includes/class-wp-comment-query.php 374
do_action_ref_array( 'pre_get_comments', array( &$this ) );

Where the hook is used (in WP core)

Does not used.