This variable is used to specify a series of directories for locating HTML template files. This variable is similar to FILE_PREFIX and CODE_PREFIX. It specifies a series of one or more directories to be searched for the desired HTML template file. The directories are specified as a sequence of space-delimited prefixes to be applied to the file name. All directories in the sequence must be valid names. The current directory can be indicated by a period (regardless of the host operating system). This is the default.