'%a'  #	Remote IP-address
    '%A'  #	Local IP-address
    '%B'  #	Size of response in bytes, excluding HTTP headers.
    '%b'  #	Size of response in bytes, excluding HTTP headers. In CLF format, i.e. a '-' rather than a 0 when no bytes are sent.
    '%D'  #	The time taken to serve the request, in microseconds.
    '%f'  #	Filename
    '%h'  #	Remote host
    '%H'  #	The request protocol
    '%k'  #	Number of keepalive requests handled on this connection. Interesting if KeepAlive is being used, so that, for example, a '1' means the first keepalive request after the initial one, '2' the second, etc...; otherwise this is always 0 (indicating the initial request). Available in versions 2.2.11 and later.
    '%l'  #	Remote logname (from identd, if supplied). This will return a dash unless mod_ident is present and IdentityCheck is set On.
    '%m'  #	The request method
    '%p'  #	The canonical port of the server serving the request
    '%P'  #	The process ID of the child that serviced the request.
    '%q'  #	The query string (prepended with a ? if a query string exists, otherwise an empty string)
    '%r'  #	First line of request
    '%R'  #	The handler generating the response (if any).
    '%s'  #	Status. For requests that got internally redirected, this is the status of the *original* request --- %>s for the last.
    '%t'  #	Time the request was received (standard english format)
    '%T'  #	The time taken to serve the request, in seconds.
    '%u'  #	Remote user (from auth; may be bogus if return status (%s) is 401)
    '%U'  #	The URL path requested, not including any query string.
    '%v'  #	The canonical ServerName of the server serving the request.
    '%V'  #	The server name according to the UseCanonicalName setting.
    '%X'  #	Connection status when response is completed:
              # X =	connection aborted before the response completed.
              #   =	connection may be kept alive after the response is sent.
              # - =	connection will be closed after the response is sent.
              # (This directive was %c in late versions of Apache 1.3, but this conflicted with the historical ssl %{var}c syntax.)
    '%I'  #	Bytes received, including request and headers, cannot be zero. You need to enable mod_logio to use this.
    '%O'  #	Bytes sent, including headers, cannot be zero. You need to enable mod_logio to use this.
    
    '%\{User-Agent\}i'  # Special case of below, for matching just user agent
    '%\{[^\}] ?\}i'  #	The contents of Foobar: header line(s) in the request sent to the server. Changes made by other modules (e.g. mod_headers) affect this. If you're interested in what the request header was prior to when most modules would have modified it, use mod_setenvif to copy the header into an internal environment variable and log that value with the %\{VARNAME}e described above.
    
    '%\{[^\}] ?\}C'  #	The contents of cookie Foobar in the request sent to the server. Only version 0 cookies are fully supported.
    '%\{[^\}] ?\}e'  #	The contents of the environment variable FOOBAR
    '%\{[^\}] ?\}n'  #	The contents of note Foobar from another module.
    '%\{[^\}] ?\}o'  #	The contents of Foobar: header line(s) in the reply.
    '%\{[^\}] ?\}p'  #	The canonical port of the server serving the request or the server's actual port or the client's actual port. Valid formats are canonical, local, or remote.
    '%\{[^\}] ?\}P'  #	The process ID or thread id of the child that serviced the request. Valid formats are pid, tid, and hextid. hextid requires APR 1.2.0 or higher.
    '%\{[^\}] ?\}t'  #	The time, in the form given by format, which should be in strftime(3) format. (potentially localized)
    '%\{[^\}] ?\}x'  # Extension value, e.g. mod_ssl protocol and cipher