Apache Reference: mod_mime_magic
mod_mime_magic - Automatic Content Type/Encoding Assignment
Since Apache 1.3, src/modules/standard/mod_mime_magic.c
Ian F. Darwin, Ian Kluft (1997)
mod_mime_magic provides for dynamic assignment of MIME content types and encodings to documents. In contrast to mod_mime, this module looks directly at the content of the document (usually its first bytes) and tries to guess the content type and encoding by matching so-called magic cookies (byte sequences that are unique to particular file formats). The resulting performance penalty should not be neglected. So this module is only reasonably used if one at the same time manually defines as many commonly known and straight-forward MIME-types as possible with
mod_mime, so mod_mime_magic only has to determine the remaining ones.