WordPress at a glance
action is not described

post-plupload-upload-ui action-hook . WP 3.3.0

Fires after the upload interface loads.

Usage

add_action( 'post-plupload-upload-ui', 'action_function_name_5080' );
function action_function_name_5080(){
	// action...
}

Changelog

Since 3.3.0 Introduced.
Since 2.6.0 As 'post-flash-upload-ui'

Where the hook is called

media_upload_form()
post-plupload-upload-ui
wp_print_media_templates()
post-plupload-upload-ui
wp-admin/includes/media.php 2086
do_action( 'post-plupload-upload-ui' );
wp-includes/media-template.php 254
do_action( 'post-plupload-upload-ui' );
wp-includes/media-template.php 258
do_action( 'post-plupload-upload-ui' );

Where the hook is used (in WP core)

wp-admin/includes/admin-filters.php 24
add_action( 'post-plupload-upload-ui', 'media_upload_flash_bypass' );
wp-includes/media-template.php 252
if ( 10 === remove_action( 'post-plupload-upload-ui', 'media_upload_flash_bypass' ) ) {
wp-includes/media-template.php 255
add_action( 'post-plupload-upload-ui', 'media_upload_flash_bypass' );