The cost of specifying MIME types or the like can easily exceed its value, which is very low because we are already specifying file types (to applications that

The cost of specifying MIME types or the like can easily exceed its value, which is very low because we are already specifying file types (to applications that can deal with more than one) well enough with file extensions (undependable, but vastly more convenient than new infrastructure for new metadata), with self-describing or recognizable file formats, and often explicitly.