In order to enable Accessible Login, the system administrator must
make some changes to the default login configuration by manually
modifying three human-readable configuration files, stored in
gdm.conf, AccessKeyMouseEvents and AccessDwellMouseEvents.
In order to allow users to change the color and contrast scheme of
the login dialog, make sure the "AllowThemeChange" parameter in
gdm.conf is set to "true".
To restrict user changes to the visual appearance to a subset of
available themes, the "GtkThemesToAllow" parameter in gdm.conf can
be set to a list of acceptable themes separated by commas.  For
example:
GtkThemesToAllow=HighContrast,HighContrastInverse
To enable the use of assistive technologies such as the Onscreen
Keyboard, Screen Reader, or Magnifier, the "AddGtkModules"
parameter in gdm.conf must be uncommented and set to "true".  Also
the "GtkModulesList" parameter must be uncommented and set as
follows:
GtkModulesList=gail:atk-bridge:dwellmouselistener:keymouselistener
System administrators may wish to load only the minimum subset of
these modules which is required to support their user base.
Depending on the end-user needs, not all of the above GtkModules
may need to be loaded.  If your end-users need the integrated
Screen Reader and Magnifier, you must include "gail" and
"atk-bridge".  If your end-users will be using a pointing device
without buttons or switches, include "dwellmouselistener".  If
some of your users will use pointing devices with switches,
alternative physical keyboards, or switch/button devices, include
"keymouselistener".  Including all four is suitable for most
system configurations.  The Onscreen Keyboard can operate without
gail and atk-bridge, but with a reduced feature set; for optimum
accessibility we recommend including gail and atk-bridge.
Once "keymouselistener" and/or "dwellmouselistener" have been
added to the GtkModules loaded by GDM, you can assign end-user
actions with the launching of specific assistive technologies.
These gesture associations are contained in files
AccessKeyMouseEvents and AccessDwellMouseEvents, respectively.
The gesture format is described in the two configuration files.
The AccessKeyMouseEvents file controls the keymouselistener
Gesture Listener and is used to define key-press, mouse button,
or XInput device sequences that can be used to launch applications
needed for accessibility.  In order to reduce the likelihood of
unintentional launch, these 'gestures' may be associated with
multiple switch presses and/or minimum durations.
The DwellKeyMouseEvents file controls the dwellmouselistner and
supports gestures that involve only motion of a pointing device
such as the system mouse of an alternative pointing device such
as a head pointer or trackball may also be defined.   All gestures
are specified by the same syntax; that is, there is no distinction
between a 'core mouse' gesture and motion from an alternate input
device.
Motion gestures are defined as "crossing events" into and out of
the login dialog window.  If the 'dwellmouselistener' GtkModule
is loaded, alternative pointing devices are temporarily "latched"
to the core pointer, such that motion from alternative devices
results in movement of the onscreen pointer.
In order to use text-to-speech services at login time (for
instance, when using the Screen Reader in speech mode) on some
operating systems, the GDM user must be made a member of the
"audio" group
