.chapter SOURCE FILE FORMAT .index Source File Format .p The source file contains the textual material that will appear on the final copy, plus information to specify formatting. All command information consists of regular ASCII printing characters, so a listing of the source file can be examined if the final copy is not exactly as desired. .p All material in the source file is taken to be source text except those lines beginning with a period. A line beginning with a period is assumed to be a command, .index Command format and must match one of those listed in the chapter on commands. The commands provide the formatting information and control various optional modes of operation.