A GDM Theme is created by specifying a hierarchy of item and box
nodes.  Item nodes can have the following value for "type":
entry
Text entry field.
list
A list widget.
label
A text label.  Must have a "text" node to specify the text.
pixmap
An pixmap image in a format that gdk-pixbuf supports like
PNG, JPEG, Tiff, etc...)
rect
Rectangle.
svg
Scaled Vector Graphic image.
For example:
<item type="label">
Items can specify ID values which gives them a specific look and feel
or formatting.  Furthermore you can customize the login process by
adding custom widgets with custom id's for some items (currently only
the list item)
Entry items can have id values as follows:
user-pw-entry
Entry field for userid and password entry.  This is the field
used for responses for the PAM/GDM questions (Username,
Password, etc..).
List items can have id values as follows:
userlist
A Face Browser list, so that users can pick
their username by clicking on this instead
of typing.
Furthermore, you can have an arbitrary id (I'd recommend starting
the id with 'custom' not to conflict with future additions to this
spec) and ask extra information of the user.  See the section
'Custom Widgetry'
Label items can have id values as follows:
clock
Label the displays the date and time.
pam-prompt
Label the displays PAM prompt.  This is the prompt that PAM
uses to ask for username, password, etc...
pam-error
Label the displays PAM/GDM error messages.  Such as when user
can't log in.
pam-message
Label the displays PAM message.  These are messages that
PAM/GDM gives about state of the account, help about the
prompts and other information.
timed-label
Label that displays timed login information.
Rectangles can have id values as follows:
caps-lock-warning
Displays an icon that shows if the
CAPS LOCK key is depressed.  This rectangle
will be hidden/shown appropriately
If an item is of type rect, the item can be a button.  Buttons
must also include a "button" value as follows:
<item type="rect" id="disconnect_button" button="true">.
Possible values for button ids are as follows:
chooser_button
Runs the XDMCP chooser.
config_button
Runs the GDM configuration application.
disconnect_button
Disconnect from remote session.
language_button
Displays the language selection dialog.
halt_button
Halt (shuts down) the system.
reboot_button
Reboot the system.
session_button
List and select from available sessions.
suspend_button
Suspend the system.
system_button
Perform halt/reboot/suspend/etc. options (if allowed by GDM
configuration).  Also allows user to run configurator if user
enters root password (again if allowed by GDM configuration).
This is usually now labeled Actions, and referred to as the
Actions menu.
