The following files are included in this category:
The file containing the image of one or two icons - a big one to be displayed as a button background and a small one to be displayed in the corresponding column of the modules list. These files are located in the <PRODUCT_ROOT_D>/admin/htdocs/modules/<module name>/images directory (see example).
Files with HTML templates for the Fast Template system <PRODUCT_ROOT_D>/admin/plib/templates/modules/<module name>/*.tpl
These templates (Plesk used FastTemplate engine) are models of text, images and control elements (buttons, lists, forms and so on) layout on pages. Placement of elements in the required places is laid on include files linked through the directive and located in the <PRODUCT_ROOT_D>/admin/htdocs/modules/<module name>/*.php directory (see example).
More information about FastTemplate engine you can find here http://www.thewebmasters.net/php/FastTemplate.phtml.