WordPress at a glance
action is not described

pre-html-upload-ui action-hook . WP 2.6.0

Fires before the upload button in the media upload interface.

Usage

add_action( 'pre-html-upload-ui', 'action_function_name_1566' );
function action_function_name_1566(){
	// action...
}

Where the hook is called

media_upload_form()
pre-html-upload-ui
wp-admin/includes/media.php 2097
do_action( 'pre-html-upload-ui' );

Where the hook is used (in WP core)

Does not used.