[Tex/LaTex] When can I safely add an empty line

line-breakingparagraphssourcecode

I really like spacing my LaTeX to stay organized, but I'm always scared that adding a space will affect the output when all I really wanted to do was separate the "code" a bit.

So most of the time I insert a "%" in the empty lines just to be safe, or I experiment. For example, I know (by playing with it) that the empty lines in the following are not doing any harm:

\documentclass{article}
\begin{document}

\title{My title}
\author{My author}
\date{\today}
\maketitle

\begin{abstract}
This is my abstract!
\end{abstract}

\section{Introduction}
Bla bla bla.
\end{document}

But I'm wondering, is there a steadfast rule that I can use to know right away if an empty line will affect output?

Best Answer

Basically, given that an empty line produces a \par token, the one rule I know is this: Empty lines are harmless when you know they (or the implied \par) will only be encountered in vertical mode. TeX starts in vertical mode, and it is in vertical mode between paragraphs, as well as at the top of many environments such as all the list environments, minipage, and floats. Also immediately after these environments (but not after a displayed equation, usually).

Related Solutions

[Tex/LaTex] Shorthand for empty line or \\ \indent

\\ produces a line break. \par produces a new paragraph. Inserting empty line between two lines produces a new paragraph.

Furthermore, \\ does not justify the last line before. If you want so you can use \linebreak.

[Tex/LaTex] Manual linebreak with justification but without empty line afterwards

if the last line of your paragraph is really nearly full, you can get it to end flush right by the following approach.

wrap the paragraph in braces.
end the paragraph with these commands (inside the braces):
```
\unskip\parfillskip 0pt \par
```

update: a mechanism that doesn't require braces.

before the paragraph, insert
```
\startsquarepar
```
at the end of the paragraph, insert
```
\stopsquarepar
```

define these two commands in the preamble as follows:

\newcommand{\startsquarepar}{%
    \par\begingroup \parfillskip 0pt \relax}
\newcommand{\stopsquarepar}{%
    \par\endgroup}

it's not necessary to have blank lines either before or after either of these commands (the grouping and included \par ensures that that's not a problem), but readability and "good practice" suggests that a blank line before \startsquarepar and one after \stopsquarepar is a good idea.

blank lines within the scope of \startsquarepar and \stopsquarepar will start new paragraphs as expected, and all paragraphs within this scope will end flush right -- whether or not there's the right amount of material in each paragraph to avoid excessive spacing.

why didn't i use \begin... and \end...? while there are no "strings" attached to \begin..., latex has co-opted the use of \end... for its own purposes in defining environments. if you really prefer the \begin ... \end terminology and environment syntax, it's easy to transform the two command definitions given into a single environment definition. (but left as an exercise to the reader.)

edit: one final suggestion from egreg's comment (to keep it from getting lost).

{{\parfillskip0pt\par}} can be a useful for a manual solution as it doesn't need bracing the paragraph.

Best Answer

Related Solutions

[Tex/LaTex] Shorthand for empty line or \\ \indent

[Tex/LaTex] Manual linebreak with justification but without empty line afterwards

Related Question