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README revision 1.1 
      1  1.1  mrg The core protocol interpretation of keyboard modifiers does not include direct
      2  1.1  mrg support for multiple keyboard groups, so XKB reports the effective keyboard
      3  1.1  mrg group to XKB-aware clients using some of reserved bits in the state field of
      4  1.1  mrg some core protocol events. This modified state field would not be interpreted
      5  1.1  mrg correctly by XKB-unaware clients, so XKB provides a group compatibility mapping
      6  1.1  mrg which remaps the keyboard group into a core modifier mask that has similar
      7  1.1  mrg effects, when possible.
      8  1.1  mrg 
      9  1.1  mrg XKB maintains three compatibility state components that are used to make
     10  1.1  mrg XKB-unaware clients(*) work as well as possible:
     11  1.1  mrg - The compatibility state which corresponds to the effective modifier and
     12  1.1  mrg   effective group state.
     13  1.1  mrg - The compatibility lookup state which is the core-protocol equivalent of the
     14  1.1  mrg   lookup state.
     15  1.1  mrg - The compatibility grab state which is the nearest core-protocol equivalent
     16  1.1  mrg   of the grab state.
     17  1.1  mrg 
     18  1.1  mrg Compatibility state are essentially the corresponding XKB states, but with
     19  1.1  mrg keyboard group possibly encoded as one or more modifiers. 
     20  1.1  mrg 
     21  1.1  mrg Modifiers that correspond to each keyboard group are described in this
     22  1.1  mrg group compatibility map.
     23  1.1  mrg 
     24  1.1  mrg 
     25  1.1  mrg ----
     26  1.1  mrg (*) The implementation of XKB invisibly extends the X library to use the
     27  1.1  mrg keyboard extension if it is present. That means, clients that use library or
     28  1.1  mrg toolkit routines to interpret keyboard events automatically use all of XKB
     29  1.1  mrg features; clients that directly interpret the state field of core protocol
     30  1.1  mrg events or the keymap direcly may be affected by some of the XKB differences.
     31  1.1  mrg Thus most clients can take all advantages without modification but it also
     32  1.1  mrg means that XKB state can be reported to clients that have not explicitly
     33  1.1  mrg requested the keyboard extension.
     34