(PECL varnish >= 0.6)
VarnishLog::TAG_Debug
     VarnishLog::TAG_Error
     VarnishLog::TAG_CLI
     VarnishLog::TAG_StatSess
     VarnishLog::TAG_ReqEnd
     VarnishLog::TAG_SessionOpen
     VarnishLog::TAG_SessionClose
     VarnishLog::TAG_BackendOpen
     VarnishLog::TAG_BackendXID
     VarnishLog::TAG_BackendReuse
     VarnishLog::TAG_BackendClose
     VarnishLog::TAG_HttpGarbage
     VarnishLog::TAG_Backend
     VarnishLog::TAG_Length
     VarnishLog::TAG_FetchError
     VarnishLog::TAG_RxRequest
     VarnishLog::TAG_RxResponse
     VarnishLog::TAG_RxStatus
     VarnishLog::TAG_RxURL
     VarnishLog::TAG_RxProtocol
     VarnishLog::TAG_RxHeader
     VarnishLog::TAG_TxRequest
     VarnishLog::TAG_TxResponse
     VarnishLog::TAG_TxStatus
     VarnishLog::TAG_TxURL
     VarnishLog::TAG_TxProtocol
     VarnishLog::TAG_TxHeader
     VarnishLog::TAG_ObjRequest
     VarnishLog::TAG_ObjResponse
     VarnishLog::TAG_ObjStatus
     VarnishLog::TAG_ObjURL
     VarnishLog::TAG_ObjProtocol
     VarnishLog::TAG_ObjHeader
     VarnishLog::TAG_LostHeader
     VarnishLog::TAG_TTL
     VarnishLog::TAG_Fetch_Body
     VarnishLog::TAG_VCL_acl
     VarnishLog::TAG_VCL_call
     VarnishLog::TAG_VCL_trace
     VarnishLog::TAG_VCL_return
     VarnishLog::TAG_VCL_error
     VarnishLog::TAG_ReqStart
     VarnishLog::TAG_Hit
     VarnishLog::TAG_HitPass
     VarnishLog::TAG_ExpBan
     VarnishLog::TAG_ExpKill
     VarnishLog::TAG_WorkThread
     VarnishLog::TAG_ESI_xmlerror
     VarnishLog::TAG_Hash
     VarnishLog::TAG_Backend_health
     VarnishLog::TAG_VCL_Log
     VarnishLog::TAG_Gzip