OpenType (OT) is a cross-platform type format that includes expert layout features to provide richer linguistic support and advanced typographic control. Using OT technology you can substitute your characters for different glyphs1 using many different methods; Ligatures, Small Caps, Oldstyle Figures, Fractions, Superscript/Subscript, Ordinals, Alternates, Titling Characters and many more.
This beginners guide will help to illustrate some of the more common features found in OT fonts and when they should be used.
Small-cap glyphs are smaller versions of normal-cap glyphs. They have many uses, but are generally used to prevent capitalised words from appearing too large when set alongside lowercase text. Another OT feature called Small Capitals From Capitals will substitute both uppercase and lowercase glyphs with small-caps and is commonly used with acronyms or abbreviations that are set amongst lowercase text.
Result: Substitutes the lowercase glyphs with small-cap glyphs.
Ligatures are designed to correct awkward character combinations where letter shapes may collide creating an unwanted effect. Expanded tracking or kerning on your text my cause any automatically placed ligatures to be removed as character collisions become less problematic.
Discretionary and Historical Ligatures
Discretionary and historical ligatures are more decorative in nature than standard ligatures and should be used sparingly for effect or to achieve an historical feel.
Result: Substitutes a specific sequence of glyphs with a ligature glyph.
Stylistic alternates are glyphs designed to give words a more animated or informal appearance and to lend more interest to type composition. Because of their decorative quality they are best used in moderation. In addition to stylistic alternatives for individual glyphs, ‘Stylistic Sets’ allow you to transform a complete body of text with predefined alternate groupings.
Result: Substitutes selected glyphs for the first stylistic alternate glyph available.
This feature substitutes glyphs with alternate glyphs based on neighbouring characters. Contextual substitutions are particularly useful when working with the more complex script typefaces which are designed to have some or all of their glyphs join.
Result: Substitutes specific glyphs with alternate glyphs based on neighbouring characters or position.
Swash glyphs are stylised letterforms with extended strokes which can be used effectively for expressive passages of text or for titles. Swashes should be used sparingly for effect. Some OT fonts also offer an option for contextual swashes that are based on neighbouring characters or position.
Result: Substitutes standard glyphs with swash glyphs.
Titling glyphs are specially designed letterforms designed for use in large titles. They have specific shapes and spacing that lend themselves to large all-cap settings.
Result: Substitutes glyphs with titling glyphs.
These glyphs are set on specific widths to give a more even type balance and colour. This is in direct contrast to tabular figures (see below).
Result: Substitutes tabular spaced figures with proportional spaced figures.
The spacing widths on these glyphs occupy exactly the same horizontal space as each other, meaning they can be aligned vertically in a very neat manner for documents that require figures in columns, such as bills or financial reports. Tabular style figures are the default figures in most fonts.
Result: Substitutes proportional spaced figures with tabular spaced figures.
These figures are numerals which share a common height. Lining figures fit better with all-cap text. Lining style figures are the default figures in most fonts.
Result: Substitutes oldstyle figures with lining figures.
These figures are designed with ascenders and descenders and have features and proportions compatible with the lowercase characters of the font, they blend in well with the optical flow and rhythm of the lowercase alphabet. (Also known as text figures)
Superior glyphs, also known as superscript, can be used for such things as footnote references, chemical compounds or mathematical exponents. Inferior characters, also known as subscript, can be used for such things as chemical compounds or also mathematical exponents.
Result: Substitutes lining or oldstyle figures with superior/inferior figures, and substitutes lowercase letters with superior/inferior letter glyphs.
This feature uses an expanded set of the most commonly used diagonal fractions to improve upon manually set fractions. Manually set fractions often use the slash to separate the numerator and the denominator, rather than the correct solidus glyph. Some OT fonts also support the creation of arbitrary fractions or stacked fractions. This feature should not be applied globally, but only where needed.
Result: Substitutes figures separated by a slash with proper fraction glyphs.
This feature provides superior letterforms that are used when creating ordinals, such as the “st”’ in 1st, “nd” in 2nd etc. The ordinal feature should not be applied globally, but only where needed. Ordinals work best with lining figures, rather than oldstyle figures, because of the constant vertical position of the ordinals.
Result: Substitutes glyphs with the corresponding ordinal forms for use after figures.
Other OpenType Features
The problem with the numeral 0 is that it can look too much like O in some typefaces. This feature will simply apply the slashed zero style to every zero.
In some languages, characters change depending on their position in a word. The options for this feature are General Form (normal glyphs), Automatic Form (glyphs are based on character position), Initial Form (first position), Medial Form (middle position), Final Form (end position), or Isolated Form (standalone position). Positional forms have little or no effect on most Latin language characters, but they may alter the behaviour of some script style typefaces.
Case Sensitive Forms
This feature shifts various punctuation marks up to a position that works better with all-cap sequences or sets of lining figures. This feature is deployed when an app’s all-caps styling is applied.
This feature adjusts the spacing for all-cap text. Most caps are positioned to work with the lowercase forms. When caps are used for words, they may require more space between them for legibility and aesthetics. This feature is deployed when an app’s all-caps styling is applied.
- Diggin’ it?! an article written by Nick Shinn just prior to OpenType, about expert typography. Nick talks about many of the classic typographic features that are now more accessible via Opentype technologies.
- A list of descriptions of the different kinds of glyphs found in Adobe OpenType fonts.
- What’s OpenType? Is it right for me?, an OpenType FAQ from Hoefler & Frere-Jones.
- Explanation of lining, old-style and tabular figures from FontShop
1. The distinction between characters and glyphs is important when discussing OpenType fonts. A character is the smallest semantic unit of a language, such as letter. A glyph is a shape or form that can be used to represent that character. For example, the character lowercase ‘a’ could be represented by a number of different glyphs including: a small-cap ‘a’, an italic ‘a’ or an alternate swash ‘a’.