The Pitfalls Of Automatic Spacing: When Xspace Goes Wrong

When xspace Fails to Add Spaces

The xspace package in LaTeX aims to automatically add spaces after commands, reducing typographic errors and manual labor for the user. However, xspace relies on appending spaces when commands are followed by punctuation. This leads to issues in specific edge cases:

Forgetting to Apply xspace at the End of Commands

The core functionality of xspace depends on applying it to custom commands with \xspace at the end. Without this declaration, xspace cannot track when a command needs trailing whitespace. A common mistake is defining macros without \xspace when it is needed:

\newcommand{\keyword}{keyword} % Forgot \xspace!

In the above example, \keyword will not automatically add spaces even if xspace is loaded. The proper definition is:

Table of Contents

\newcommand{\keyword}{keyword}\xspace

New users of xspace must train themselves to add \xspace consistently. For large documents or codebases, it can be tedious to audit all command declarations. Debugging spacing issues from a missing \xspace can also be tricky.

Nested Commands Causing Duplicate Spaces

xspace relies on appending spaces after punctuation. However, if multiple xspace-enabled commands are nested, each invocation may append an extra space:

We analyzed the \keyword{distribution models} regarding the dataset.

Here, \keyword adds a trailing space due to the period after it. But the outer sentence also ends with a period that inserts another space. The output contains a double space between "models" and "regarding," which is typographically incorrect.

This issue arises frequently when combining xspace commands with other punctuation. It grows more severe for deeply nested command structures. Each level can compound extra spaces, requiring manual intervention to correct.

Incompatibilities with Other Packages

The automation of xspace relies on appending implicit space tokens after commands. However, other LaTeX packages may fail to accommodate these implicit spaces in their own automated rules. For example, citations often break when used after xspace macros:

The theory has origins in \keyword{divergence analysis} \cite{Lee2018}.

Here, the citation command may fail because the implicit space after \keyword comes between it and its internal label. This causes a LaTeX error even though the syntax looks correct.

Such technical incompatibility issues are unpredictable. Each package sets its own string parsing rules that may not expect stray whitespace. Thus xspace has many little-known conflicts across different LaTeX ecosystem tools.

Fixing xspace Errors

When xspace spacing problems emerge in documents, there are closed-form fixes to remedy issues without fully removing xspace:

Manually Adding {} or \

Curly braces {} and backslash escapes are both used to tell LaTeX to avoid applying automated tokenization rules. Adding these after xspace commands prevents improper whitespace insertion:

We analyzed the \keyword{distribution models{}\cite{Lee2018}} regarding...\keyword{convergence rate\ }metrics.

Here, the {} and \ manually override xspace's automatic space injection to fix the citation and metric spacing. This is the fastest patching method without altering xspace behavior globally.

Using xspace’s Safe Option

xspace has a "safe" mode that adds \relax before each space token. \relax stops chains of automated parsing. This prevents issues with nested commands and package clashes:

\usepackage[safe]{xspace}
We analyzed the \keyword{distribution models} \cite{Lee2018} regarding \keyword{convergence rate} metrics.

However, safe mode adds overhead to process the \relax injections. It may also interfere with desired typography from other commands. Safe mode trades robustness for guaranteed spacing correctness.

Patching Commands with \xpatchcmd

LaTeX provides \xpatchcmd from the etoolbox package to directly rewrite command definitions. For recurring xspace issues, fixes can be applied once at the macro level:

\xpatchcmd{\keyword}{\xspace}{}{}{Failed to patch \keyword}
\newcommand{\keyword}{keyword}

Here, \keyword is modified to remove its trailing \xspace call entirely. This no longer invokes xspace's automatic behavior. Patching proactively avoids problems, but loses xspace protection if not applied judiciously.

Best Practices for xspace

To leverage xspace robustly, authors should follow certain design principles in usage:

Apply Selectively After Testing

Attaching xspace broadly without testing often causes insidious spacing bugs. The safest approach is to define commands without it, then incrementally apply it later once spacing is verified:

\newcommand{\keyword}{keyword} % no xspace initially
\usepackage{xspace} 
%\xspaceaddexceptions{\keyword} % Add later if spacing works

Conservatively applying xspace allows easier debugging compared to removing it after-the-fact. Precision inclusion also prevents overhead from redundant \relax injections in safe mode.

Use noopsz to Avoid Spaces in Math Mode

xspace is designed for text spacing only. In math mode, its spaces disrupt syntax and output. noopsz wraps a command to avoid spacing in math contexts:

\newcommand{\diff}{\ensuremath \mathrm{d}}\xspace
\renewcommand{\diff}{\Noopsz\diff} % Disable spacing in math

This ensures typographic correctness without manual mode switching. Particularly for physics and engineering, noopsz prevents xspace pitfalls with equations.

Set a Reminder to Manually Check Output

Automatic xspace features can silently inject flaws like double spaces over time. Periodically scanning documents identifies new spacing issues:

% TODO: Check xspace behavior on 2023-06-30 before next release
\newcommand{\kw}[1]{#1}\xspace

Regular manual review catches small problems before they scale up. As new packages and commands are added, spacing may gradually drift without proactive checking.