Universal Subtitle Format (USF) was a CoreCodec project that attempted to create a clean, documented, powerful and easy to use subtitle file format. It is based on XML for flexibility, unicode support, hierarchical system, and ease of administration. USF subtitles are usually used in Matroska containers. No known media player software implements more than basic support for this format. VSFilter, and VLC media player (starting with the 0.9.0 release) can extract the subtitle text, timing information and very restricted formatting.