This is documentation about a configuration directive, which can be placed within Movable Type’s core configuration file,
mt-config.cgi, to customize the behavior of the system.
In most cases, using with SupportDirectoryPath, Sets the publish URL for the support directory.
MT uploads asset files for CMS, for example, Userpics or theme thumbnails to support directory. To change the directory, need to make the directry and grant permission to write, in advance.
An absolute or relative URL