File: groff.info,  Node: Input Conventions,  Prev: Input Encodings,  Up: Text

5.1.10 Input Conventions
------------------------

Since GNU 'troff' fills text automatically, it is common practice in the
'roff' language to avoid visual composition of text in input files: the
esthetic appeal of the formatted output is what matters.  Therefore,
'roff' input should be arranged such that it is easy for authors and
maintainers to compose and develop the document, understand the syntax
of 'roff' requests, macro calls, and preprocessor languages used, and
predict the behavior of the formatter.  Several traditions have accrued
in service of these goals.

   * Follow sentence endings in the input with newlines to ease their
     recognition (*note Sentences::).  It is frequently convenient to
     end text lines after colons and semicolons as well, as these
     typically precede independent clauses.  Consider doing so after
     commas; they often occur in lists that become easy to scan when
     itemized by line, or constitute supplements to the sentence that
     are added, deleted, or updated to clarify it.  Parenthetical and
     quoted phrases are also good candidates for placement on text lines
     by themselves.

   * Set your text editor's line length to 72 characters or fewer.(1)
     (*note Input Conventions-Footnote-1::) This limit, combined with
     the previous item of advice, makes it less common that an input
     line will wrap in your text editor, and thus will help you perceive
     excessively long constructions in your text.  Recall that natural
     languages originate in speech, not writing, and that punctuation is
     correlated with pauses for breathing and changes in prosody.

   * Use '\&' after '!', '?', and '.' if they are followed by space,
     tab, or newline characters and don't end a sentence.

   * In filled text lines, use '\&' before '.' and ''' if they are
     preceded by space, so that reflowing the input doesn't turn them
     into control lines.

   * Do not use spaces to perform indentation or align columns of a
     table.  Leading spaces are reliable when text is not being filled.

   * Comment your document.  It is never too soon to apply comments to
     record information of use to future document maintainers (including
     your future self).  We thus introduce another escape sequence,
     '\"', which causes GNU 'troff' to ignore the remainder of the input
     line.

   * Use the empty request--a control character followed immediately by
     a newline--to visually manage separation of material in input
     files.  Many of the 'groff' project's own documents use an empty
     request between sentences, after macro definitions, and where a
     break is expected, and two empty requests between paragraphs or
     other requests or macro calls that will introduce vertical space
     into the document.

     You can combine the empty request with the comment escape sequence
     to include whole-line comments in your document, and even "comment
     out" sections of it.

   We conclude this section with an example sufficiently long to
illustrate most of the above suggestions in practice.  For the purpose
of fitting the example between the margins of this manual with the font
used for its typeset version, we have shortened the input line length to
56 columns.  As before, an arrow -> indicates a tab character.

     .\"   nroff this_file.roff | less
     .\"   groff -T ps this_file.roff > this_file.ps
     ->The theory of relativity is intimately connected with
     the theory of space and time.
     .
     I shall therefore begin with a brief investigation of
     the origin of our ideas of space and time,
     although in doing so I know that I introduce a
     controversial subject.  \" remainder of paragraph elided
     .
     .

     ->The experiences of an individual appear to us arranged
     in a series of events;
     in this series the single events which we remember
     appear to be ordered according to the criterion of
     \[lq]earlier\[rq] and \[lq]later\[rq], \" punct swapped
     which cannot be analysed further.
     .
     There exists,
     therefore,
     for the individual,
     an I-time,
     or subjective time.
     .
     This itself is not measurable.
     .
     I can,
     indeed,
     associate numbers with the events,
     in such a way that the greater number is associated with
     the later event than with an earlier one;
     but the nature of this association may be quite
     arbitrary.
     .
     This association I can define by means of a clock by
     comparing the order of events furnished by the clock
     with the order of a given series of events.
     .
     We understand by a clock something which provides a
     series of events which can be counted,
     and which has other properties of which we shall speak
     later.
     .\" Albert Einstein, _The Meaning of Relativity_, 1922