Its purpose is to provide an implementation guideline for producers of fonts for the representation of European natural languages; fonts that provide glyphs for the entire set of characters can claim WGL4 compliance and thus can expect to be compatible with a wide range of software.
As of 2004[update], WGL4 characters were the only ones guaranteed to display correctly on Microsoft Windows.
More recent versions of Windows display far more glyphs.
It also does not cover the Romanian letters Ș, ș, Ț, and ț (U+0218–B), which were added to several of Microsoft's fonts for Windows Vista (long after the WGL4 repertoire was originally defined).
In version 1.5 of the OpenType Specification (May 2008) four Cyrillic characters were added to the WGL4 character set: Ѐ (U+0400), Ѝ (U+040D), ѐ (U+0450) and ѝ (U+045D).