OpenType features

By Stefan Peev, July 24, 2018

Why we need to understand OpenType features

Much of the font creator programs offer nowadays simplified ways to create OpenType features. But when the things go wrong these programs could not help us. So we need to understand the structure, the logic and the syntax of the OpenType features.
Like in every other process, which we want to know how to rule, we need to start with some learning. Here are the basic resources for OpenType features.

Tal Leming: OpenType Cookbook
Martin Wenzel, Christoph Koeberlin: An Introduction to OpenType Substitution Features
Glyphs: Tutorials Tagged “OpenType Features”

Please, note that even well written OpenType features could not work. Why? Because the use of OpenType features relies on your applications’ support. Click here to see OpenType features’ support in applications. Check here for the browsers’ support for font-feature-settings.

Glyph substitution (GSUB) rules

GSUB

LookupType 1
Single substitution

aalt abvf c2pc c2sc case cfar cv01-cv99 dcap dnom dtls expt fin2 fin3 fina flac frac fwid hist hkna hngl hojo hwid init isol ital jajp jp04 jp78 jp83 jp90 ljmo lnum locl ltra ltrm med2 medi mgrk nalt nlck numr onum ornm pcap pnum pwid qwid rtla rtlm ruby rvrn salt sinf smcp smpl ss01-ss20 ssty subs sups swsh titl tjmo tnam tnum trad twid unic vert vjmo vkna vrt2 vrtr zero

GSUB

LookupType 2
Multiple substitution

ccmp stch RQD

GSUB

LookupType 3
Alternate substitution

aalt falt hngl jalt jajp jp78 nalt ornm rand salt ssty swsh trad RQD

GSUB

LookupType 4

Ligature substitution

GSUB LookupType 5

Contextual substitution

GSUB LookupType 6

Chaining contextual substitution

6.1.

GSUB LookupType 6

Specifying a Chain Sub rule and marking sub-runs

6.2.

GSUB LookupType 6

Specifying exceptions to the Chain Sub rule

GSUB LookupType 7

Extension substitution

GSUB LookupType 8

Reverse Chaining Single Substitution

1. [GSUB LookupType 1] Single substitution
2. [GSUB LookupType 2] Multiple substitution
3. [GSUB LookupType 3] Alternate substitution
4. [GSUB LookupType 4] Ligature substitution
5. [GSUB LookupType 5] Contextual substitution
6. [GSUB LookupType 6] Chaining contextual substitution
6.1. Specifying a Chain Sub rule and marking sub-runs
6.2. Specifying exceptions to the Chain Sub rule
7. [GSUB LookupType 7] Extension substitution
8. [GSUB LookupType 8] Reverse Chaining Single Substitution

OpenType Features

feature numr

feature dnom

feature frac

feature sups

feature subs

feature sinf

feature ordn

feature tnum

feature onum

feature pnum

feature lnum

feature zero

feature locl
Bulgarian Cyrillic – .loclBGR
Serbian Cyrillic – .loclSRB
Macedonian Cyrillic – .loclMKD
Bashkir Cyrillic – .loclBSH
Chuvash Cyrillic – .loclCHU
Romanian Latin – ROM
Moldovan Latin – MOL
Turkish Latin – TRK

feature ccmp

feature case

feature c2sc

feature smcp

feature liga

feature dlig

feature calt

Glyph Name Suffixes

Feature Name/Description

Feature Tag

Glyph Suffixes

SMALL CAPS

smcp

.sc .smcp .small

OLDSTYLE FIGURES

onum

.osf .oldstyle

TABULAR FIGURES

tnum

.tf

PROPORTIONAL FIGURES

pnum

.lf .fitted

TABULAR OLDSTYLE FIGURES

.tosf .taboldstyle

SUPERIORS

sups

.sups .superior

INFERIORS

sinf

.sinf .inferior

NUMERATORS

numr

.numr .numerator

DENOMINATORS

dnom

.dnom .denominator

CASE ACCENTS

case

.case .cap

CAPITALS TO SMALL CAPS

c2sc

.c2sc

OpenType Classes and Glyphs in the classes

Class names

Glyphs in the class

[zero one two three four five six seven eight nine]

osf

[zero.osf one.osf two.osf three.osf four.osf five.osf six.osf seven.osf eight.osf nine.osf]

[zero.tf one.tf two.tf three.tf four.tf five.tf six.tf seven.tf eight.tf nine.tf]

tosf

[zero.tosf one.tosf two.tosf three.tosf four.tosf five.tosf six.tosf seven.tosf eight.tosf nine.tosf]

lfPunct

[space period comma]; # original

osfPunct

[space.osf period.osf comma.osf]; # identical to original

tfPunct

[space.tf period.tf comma.tf]; # by Lining Tabular width

tosfPunct

[space.tosf period.tosf comma.tosf]; # by Oldstyle Tabular width

Why we need to understand OpenType features

Glyph substitution (GSUB) rules

OpenType Features

Glyph Name Suffixes

OpenType Classes and Glyphs in the classes

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