Opens or closes the preview of a project page or macro
| Parameter | Description | 
|---|---|
| PROJECTNAME | Name of the project. If the path is missing, the default value is used (see $(MD_PROJECTS)) | 
| PAGENAME | Name of page as string | 
| MACRONAME | Complete path to a window or page macro (with extension). If the path is missing, the default value is used (see $(MD_MACROS)) | 
| SHOW | 1: The preview of the page/macro will be opened.
                0: The preview will be closed.
 | 
If PAGENAME and MACRONAME are empty, all pages of the project will be displayed in the preview