The third section of termset describes various terminal parameters. These include the number of lines and columns on the terminal screen and what the fill characters should be for REVERSE VIDEO and UNDERLINE fields.
When defining the number of lines and columns on the terminal screen, you must key-in the number followed by a RETURN. When defining the fill characters, however, only the character-key itself is allowed. For terminals that have display attributes, these fill characters should be blanks. For terminals that do not have display attributes, the fill characters should be two distinct characters that will demarcate data fields. The characters normally used in this case are the underscore (_) for REVERSE VIDEO fields and the period (.) for UNDERLINE fields.
When running C/Base programs which use display attributes on a terminal that has no display attributes, the program simply writes on the screen the appropriate number of fill characters to represent the field. As each field is entered, the fill characters are replaced by what is typed. In this way, it is possible to use C/Base programs such as those which create and utilize data entry screens on terminals that do not have reverse video and underlining display capabilities.
After all of the various sequences have been defined, termset asks if the cycle should be repeated. This should be done if there are mistakes to be corrected. If you respond with n, termset writes the definition to the file named by the terminalname argument and exits.