Latex Ligatures And Spacing: Preventing Unintended Consequences

Troublesome Ligatures and Spacing

In LaTeX, ligatures are specific combinations of letters that are rendered as single glyphs to improve text flow and readability. Common ligatures include combining "f" and "i" into a single glyph when positioned adjacent to each other in a word. Letterspacing refers to the horizontal space between letters in a line of text.

While ligatures and fine-tuned letterspacing can greatly enhance the typographic quality of a document, improper use can also lead to unintended and potentially meaning-altering consequences in the rendered output.

What are ligatures and letterspacing in LaTeX?

Ligatures are visual replacements of letter combinations like "fi", "ff", "fl" etc. with a single glyph that improves readability and takes up less space on a line. For example, LaTeX might render the "fi" in "traffic" using a ligature that connects the f and i visually into one amalgamated glyph shape instead of two separate letters. Such ligature replacements are applied automatically by the LaTeX typesetting engine based on enabled font typefaces and supported glyph variants.

Table of Contents

Letterspacing refers to the horizontal spacing inserted between characters in a line of text, specified as extra horizontal "width" that is added between each grapheme or letter. Wider letterspacing can help improve readability for certain fonts and contexts, but too much letterspacing leads to text that looks mechanically spaced out. LaTeX provides multiple methods of fine-tuning spacing around letters, especially for purposes like adding more spacing before or after punctuation symbols.

Common issues with ligatures and spacing

Incorrect ligature usage

If certain ligatures get applied in unintended contexts, they can significantly alter the semantic meaning and flow of text. For example, an "fl" ligature in the word "flow" is typically harmless and even aesthetically enhancing. But an "fl" ligature in the word "inflate" would be inappropriate and potentially confusing for readers.

Likewise, ligatures that work for specific words when used in isolation may look odd or unintelligible when those words appear as substrings in longer technical strings and code snippets. For example the "fi" ligature would break variable strings like "wifi_strength" or file sequence patterns like "doc_v1-final-final.tex".

Unintended large spaces between letters

The default letterspacing used by LaTeX between all characters is designed for optimal readability of body paragraphs. But for specialized contexts like code listings, URLs, file names etc., the default inter-letter spacing can end up looking oddly wide without manual customization.

For example, file names like "My Long File Name v2.tex" don't look right when LaTeX applies default spacing suited for prose text between each letter. Similarly for strings like XML tags and code snippets, default spacing breaks the tight, uniform styling needed for reliable technical typesetting.

Preventing unintended ligature effects

The \” command to disable specific ligatures

To selectively prevent ligatures in specific letter combinations like "fi" and "ff", LaTeX provides the \" escape sequence. By placing this command between letters where incorrect ligature glyphs may get applied, it effectively "cancels" the ligature to render using normal letter spacing instead.

For example adding \" before "f" in both these words prevents "fi" and "ff" ligatures respectively:

traf\"fic 

dif\"ference

The \textls command for custom letterspacing

To override LaTeX's default spacing between all letters, the \textls from the microtype package can be used. This command takes a spacing length parameter that customizes inter-letter spacing.

For example, adding \textls[50] tightens up spacing by 50% relative to default spacing for uniform styling of long strings and code:

\textls[50]{thisstringhascustomspacing}

Best practices for ligature and spacing control

Define custom commands for disabling ligatures

For frequent cases disabling ligatures and letterspacing, useful shortcuts are defining custom commands once that can be reused. For example:

\newcommand{\noligs}[1]{\textls[50]{\"\i #1}}

Will create a \noligs command that disables "fi" ligatures and tightens letterspacing, to then be used as:

\noligs{filenamestrings}

Set explicit spacing around punctuation

For specific punctuation marks like periods, commas etc. prone to cause unintended large gaps in contexts like filenames and URLs, per-symbol spacing can be manually overridden:

my\,.file\,-name\.tex

This will render the punctuation with no extra spacing beyond the normal inter-word spacing.

Example LaTeX code showing ligature and spacing techniques

% Disable f-ligatures and reduce spacing 
\newcommand{\codestyle}[1]{\textls[50]{\"\i #1}}

% Tight spacing around punctuation
\newcommand{\tightpunct}[1]{\\.#1\,}

\codestyle{This_is_a_code_example} 

\tightpunct{my-file-name.tex}

The above code defines custom commands for ligature prevention and spacing overrides, demonstrating their usage for strings requiring specialized typesetting.

Summary

Key points on managing ligatures and spacing

Ligatures can cause unintended rendering issues when incorrectly applied
Default letterspacing may look too wide for code and filenames
Use \" and \textls to override default LaTeX spacing behavior
Custom commands streamline ligature and spacing management
Manual spacing around punctuation prevents large gaps

Additional resources for fine-tuned text formatting

For more advanced font and typography control in LaTeX, refer to documentation on:

The microtype package for additional spacing/ligature commands
Working with OpenType fonts and features
Font expansion/compression basics
Letterspacing best practices