This specification describes a collection of X private protocols that allow multiple X clients to communicate and coordinate their operation with a compliant window manager to independently operate different parts of that window manager. In simple terms: MetaClients are the 'modules' of a modular window manager, and this specification allows their communication.
The following protocols are defined by the Window Manager MetaClients specification. So-called MetaClients MAY implement one or more of these protocols, however it is RECOMMENDED that no more than one protocol is implemented by one MetaClient.
Window managers MUST be prepared to accept any MetaClient to communicate with any of the protocols
that the window manager supports and that are listed in the MetaClient's WM_PROTOCOLS property.
Window managers MAY NOT choose to accept communication over protocols that were not present in the
MetaClient's WM_PROTOCOLS property when the window manager first read that property. MetaClients
MUST provide all WMMC protocols that they SHALL communicate over in their WM_PROTOCOLS property.
MetaClients MUST fulfill the requirements of all WMMC protocols which they provide in the
WM_PROTOCOLS property.
The _WMMC_LAYOUT protocol allows for the communication between a separate 'layout manager' for
tiling window managers, and the window manager itself.
The _WMMC_DECORATE protocol allows the decoration of windows (i.e. titlebars, borders, etc.)
independent of the window manager, meaning a consistent visual style can be maintained across
window managers.
In the _WMMC_DECORATE protocol, window decorations can be considered to be aligned either inside
or outside the space allocated for the window by the window manager. This is particularly useful
when comparing floating and tiling layouts: in a floating window layout, it might make sense that
window decorations are always 'added' to a window; they extend the area occupied by the window, so
that they are not shrinking the window being decorated, however it might make more sense in a
tiling window layout, where space is 'strictly' allocated to windows, that a window and its
decorations never take up more or less room than is allocated by the window manager.
A window manager participating in the _WMMC_DECORATE protocol SHALL send a _WMMC_DECORATE event
to exactly one _WMMC_DECORATE client. This event SHALL contain the identifier for the window that
shall be decorated, the new width and height allocated by the layout to this window (or, if not,
the current width and height of the window), and a boolean value representing the alignment of
window decorations, with 0/false representing that decorations SHALL be placed outside the
decorated window, and 1/true representing that decorations SHALL be placed inside the decorated
window. The window manager SHALL NOT include any x or y position with this event; these fields
MUST be set to 0, and are only for _WMMC_DECORATE clients to send events to the window manager.
If decorations are aligned outside the allocated space, the size of the window is fixed and the
frame created by the decorator (i.e. the _WMMC_DECORATE client) MUST be at least the same width
and height, plus any x or y offset of the frame, as the decorated window. In this case, the
decorator MUST send a _WMMC_DECORATE event back to the window manager indicating the position
(x and y unsigned offsets from the top-left of the decorated window; ie. window_x - frame_x
and window_y - frame_y) and size (width and height) of the created frame. The _WMMC_DECORATE
event sent to the window manager MUST also include the window ID of the created frame.
If decorations are aligned inside the allocated space, the size of the window decorations frame is
fixed and MUST be created by the decorator according to the exact width and height provided by the
window manager. In this case, the decorator MUST send a _WMMC_DECORATE event back to the window
manager indicating the position (relative to the frame's top-left corner) and size to apply to the
decorated window when placing it within the frame. The _WMMC_DECORATE event sent to the window
manager MUST also include the window ID of the created frame.
The _WMMC_CONFIG protocol allows for the universal configuration of compliant window managers. It
separates the mode of configuration (for example, a config file or shell commands) from the window
manager and allows the user to choose the type of configuration which they prefer.
The _WMMC_INPUT protocol allows for the separation between the mode of input, and specific input
bindings, from the functionality of the window manager. The 'keybindings', as well as other types
of input, can be configured and new modes of input can be introduced without requiring changes to
the window manager.