Filters
    This document describes the use of filters in Apache.
  
    
    
    A filter is a process that is applied to data that
    is sent or received by the server. Data sent by clients to the
    server is processed by input filters while data sent
    by the server to the client is processed by output
    filters. Multiple filters can be applied to the data, and
    the order of the filters can be explicitly specified.
    Filters are used internally by Apache to perform functions such
    as chunking and byte-range request handling. In addition, modules
    can provide filters that are selectable using run-time
    configuration directives. The set of filters that apply to data
    can be manipulated with the
    SetInputFilter,
    SetOutputFilter,
    AddInputFilter,
    AddOutputFilter,
    RemoveInputFilter, and
    RemoveOutputFilter
    directives.
    The following user-selectable filters are currently provided
    with the Apache HTTP Server distribution.
    
      - INCLUDES
- Server-Side Includes processing by mod_include
- DEFLATE
- Compress output before sending it to the client using
          mod_deflate
In addition, the module mod_ext_filter allows
    for external programs to be defined as filters.