Helps when the "Content-Type" header is not configured in the "Section"
indexer.conf command, and thus is not stored in the database.
When generating excerpts using Cached Copy, search.cgi
tries first to fetch Content-Type information from the database.
If it's not found, search.cgi tries to detect Content-Type automatically
using some well-know substrings like
in the beginnig of the
document, unpacked from Cached Copy. If automatic guesser fails to detect
the document type, it chooses "text/plain" by default. You can change the
default value to "text/html" or "text/xml". But usually, a better
idea (if you use Cached Copies) is to activate storing Content-Type
using a proper "Section" command in indexer.conf.