The webmaster can set and remove HTTP response headers for special purposes, such as setting metainformation for an indexer, or PICS labels. Note that Apache doesn't check whether what you are doing is at all sensible, so make sure you know what you are up to, or very strange things may happen.
HeaderName [set|add|unset|append] HTTP-header "value" HeaderName remove HTTP-header Anywhere
The HeaderName directive takes two or three arguments: the first may be set, add, unset, or append; the second is a header name (without a colon); and the third is the value (if applicable). It can be used in <File>, <Directory>, or <Location> sections.