It is based on XML for flexibility, unicode support, hierarchical system, and ease of administration.
The format has come under criticism, especially from the fansub community,[2] because compared to the format it aimed to replace, Advanced Substation Alpha (which is based on comma-separated values), it is more verbose and far harder for software to read, write and manipulate.
Also, it is not easily human readable and much harder to edit "by hand" in text editors such as Notepad.
For these reasons, as well as the lack of a generic cross-platform parsing/rasterizing library and mature editing programs that natively support it, the format has not gained wide acceptance.
VSFilter, and VLC media player (starting with the 0.9.0 release) can extract the subtitle text, timing information and very restricted formatting.