哪位高手懂 RewriteHeader 指令

谁懂 RewriteHeader 指令
To   remove   header,   format   string   pattern   should   generate   an   empty   string.   For   example   this   rule   will   remove   user   agent   information   from   the   client   request:

RewriteHeader   User-Agent:   .*   $1
 

And   this   rule   will   add   Old-URL   header   to   the   request,   providing   a   Request-URL   as   a   header   value:

RewriteCond   URL   (.*)
RewriteHeader   Old-URL:   ^$   $1
 

This   last   example   will   direct   all   WebDAV   requests   to   the   /webdav.asp   script   by   changing   request   method:

RewriteCond   METHOD   OPTIONS
RewriteRule   (.*)   /webdav.asp?$1
RewriteHeader   METHOD   OPTIONS   GET
 
能给我解释一下么
弄不明白

[解决办法]
不懂