User`s manual

Conversion Process
83
OpenType Features
OpenType fonts consist of multiple tables. Every table is identified by a tag,
which is a combination of up to 4 characters.
3 tables are “responsible” for the OpenType features:
GDEF
Glyph definition table. Contains information about font glyphs, including
their type (simple, mark or ligature), cursive-attachment points and
position of the caret inside the ligature character.
GSUB
Glyph substitution features
GPOS
Glyph positioning features
Other tables may exist in OpenType fonts, for example the BASE table that
defines different baseline positions for non-Roman scripts, but TransType
Pro doesn't work with these tables.
Information about OpenType features is stored in a binary form inside the
font file. When TransType opens an OpenType font file that contains
features it tries to reconstruct the feature-definition file.
Please note that the presence of any one of these tables makes a TrueType
font an OpenType TT font.