Use it to determine which browsers need to load additional fonts in order to render text on the page.
https://github.com/Modernizr/Modernizr/blob/master/feature-detects/unicode.js
See also unicode-range feature detection and relevant spec:
https://github.com/Modernizr/Modernizr/blob/master/feature-detects/unicode-range.js
http://www.w3.org/TR/2013/CR-css-fonts-3-20131003/#descdef-unicode-range
Version: unspecified
Severity: normal
It is not that easy as we imagine, unfortunately.
It is documented it in detail here:
https://www.mediawiki.org/wiki/Universal_Language_Selector/WebFonts#Font_detection (Also in the FAQ section of that document)
ULS webfonts apply fonts by default to a subset of languages that it supports. This list of languages is given at https://www.mediawiki.org/wiki/Universal_Language_Selector/WebFonts#Table_of_languages_and_default_fonts
Each of this language is chosen based on community requests. Each language has their own reasons to choose default font embedding and reason for choosing a particular font. For all other languages, nothing happens unless user choose a font using preferences UI.
The bug reports causing default webfonts for the above set of languages is documented inside the code too. Eg: https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FUniversalLanguageSelector/23c961e4ba812ae75c791d7d31c9bb74f0a037c9/data%2Ffontrepo%2Ffonts%2FShapour%2Ffont.ini#L6