[css-fonts] Add generic font family, Blackletter

[Crissov]

https://www.w3.org/TR/css-fonts/#generic-font-families

Per #8128, #4566 and #4910, I would like to propose a new generic font family for the blackletter font style, which is still sometimes used for headings and other decorative text in German and some other European languages.

This style with broken glyph shapes – as if written with a broad quill – is also known by the names of some prominent implementations, Fraktur in particular. Other important variants include Schwabacher, Textura/Textualis, Rotunda, Gothic and more. It may therefore be acceptable to introduce, for instance, generic(fraktur) instead of generic(blackletter) or generic(black-letter).

For many users, the actual typeface used is of secondary importance because they primarily want a distinct look deviating from the now default “grotesque” Antiqua style. Besides evoking associations with traditionalism and conservatism, e.g. in newspaper logos and headlines, it has also been popular in some subcultures, e.g. in the heavy metal music genre and in graffiti / hip-hop culture.

Since its look is originally informed by the handwriting medium used, which then had been adopted for printing beginning with Gutenberg, styles with similar characteristics were also developed for other scripts than Latin. However, it is expected that the only ones potentially be also covered by readily available fonts are Cyrillic and, less likely, Greek.

ISO 15924 includes the script code Latf = 217 Latin (Fraktur variant) and Unicode includes two mathematical alphabets with Fraktur glyphs.

Especially in printed German texts before the mid-20th century, intricate typographic conventions were developed that differ from those used with Antiqua texts. These largely still apply when typesetting in this style. For instance, emphasis was preferably expressed by letter-spacing (or perhaps underlining) instead of bold-facing or italics.

Unfortunately, no major vendor (Microsoft, Apple, Google) seems to bundle a blackletter font with their operating system or browser yet. Some versions of Microsoft Office ship with Old English Text MT, which would be acceptable.

[Crissov]

I considered to copy some of this text into a new issue to request generic(uncial) independently, but I believe the use cases are similar enough to be handled together with generic(blackletter). I’m not sure whether Gaelic and insular should be subsumed under that umbrella term.