.chapter SOURCE FILE FORMAT
.index Source File Format 
.p
The source file contains the textual material 
which will appear on the final copy, plus information to 
specify formatting.  All command information consists 
of regular ASCII printing characters so that a listing of 
the source file may 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, 
.comment index Command format 
and must match one 
of those listed in chapter 4.  The commands provide the formatting 
information, and control various optional modes of operation. 
.p 
Usually the text is filled 
.index Filling of text 
and justified 
.index Justification of text 
 as it is processed. 
That is, the program FILLS a line by adding successive words 
from the source text until one more word would cause the right 
margin to be exceeded.  The line is then JUSTIFIED by 
making the word spacings larger until the last word in the line 
exactly meets the right margin. 
.p 
The user may occasionally wish to reproduce the source text
.index Literals
exactly, which is done by 
disabling filling and justification or by use of the LITERAL 
command. The program may be set 
to fill but not justify, in which case the output will be  
normal except that lines will not be justified to the right margin. 
The program may also be set to justify but not fill,  
although this would probably produce peculiar results and 
is not recommended. 
.p 
When the fill mode is on, spaces, 
.index Space 
.index Word spacing 
and carriage returns  
occurring in the source text are treated only as word 
separators.  Multiple separators are ignored. 
In addition an extra space is added to punctuation occurring at the end 
of a sentence. 
.p 
Some of the commands cause a BREAK 
.index BREAK 
in the output. A break means that the current line is output without 
justification, and the next word goes at the beginning 
of the next line.  This occurs at the end of paragraphs. 
.p 
The program will advance to new pages as necessary, placing 
.index Page Numbering 
.index Title 
the title (if given) and the page number at the top of each 
page.  The user may call explicitly for a page advance where 
desired, and may inhibit the occurrence of a page advance 
within specified material.