1. Font files, format and information
A font is a collection of various character images that can be used to display or print text. The images in a single font share some common properties, including look, style, serifs, etc. Typographically speaking, one has to distinguish between a font family and its multiple font faces, which usually differ in style though come from the same template.
For example, ‘Palatino Regular’ and ‘Palatino Italic’ are two distinct faces from the samefamily, called ‘Palatino’ itself.
The single term ‘font’ is nearly always used in ambiguous ways to refer to either a given family or given face, depending on the context. For example, most users of word-processors use ‘font’ to describe a font family (e.g. ‘Courier’, ‘Palatino’, etc.); however, most of these families are implemented through several data files depending on the file format: For TrueType, this is usually one per face (i.e. arial.ttf for ‘Arial Regular’, ariali.ttf for ‘Arial Italic’, etc.). The file is also called a ‘font’ but really contains a font face.
A digital font is thus a data file that may contain one or more font faces. For each of these, it contains character images, character metrics, as well as other kind of information important to the layout of text and the processing of specific character encodings. In some formats, like Adobe's Type 1, a single font face is described through several files (i.e., one contains the character images, another one the character metrics). We will ignore this implementation issue in most parts of this document and consider digital fonts as single files, though FreeType 2 is able to support multiple-files fonts correctly.
As a convenience, a font file containing more than one face is called a font collection. This case is rather rare but can be seen in many Asian fonts, which contain images for two or more representation forms of a given scripts (usually for horizontal and vertical layout.
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