indexing
	description: "Node for use with EV_TREE."
	status: "See notice at end of class"
	keywords: "tree, item, leaf, node, branch"
	date: "$Date$"
	revision: "$Revision$"

deferred class interface
	EV_TREE_NODE

feature -- Initialization

	frozen default_create
			-- Standard creation procedure.
			-- (from EV_ANY)
		ensure then -- from EV_ANY
			is_coupled: implementation /= void
			is_initialized: is_initialized
			default_create_called_set: default_create_called
			is_in_default_state: is_in_default_state
	
feature -- Access

	accept_cursor: EV_CURSOR
			-- Result is cursor displayed when the screen pointer is over a
			-- target that accepts pebble during pick and drop.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.accept_cursor

	alignment: EV_TEXT_ALIGNMENT
			-- Current text positioning.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			alignment_not_void: Result /= void

	data: ANY
			-- Arbitrary user data may be stored here.
			-- (from EV_ANY)

	deny_cursor: EV_CURSOR
			-- Result is cursor displayed when the screen pointer is over a
			-- target that does not accept pebble during pick and drop.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.deny_cursor

	find_item_recursively_by_data (v: ANY): EV_TREE_NODE
			-- An item at any level in tree that has data.
		require
			not_destroyed: not is_destroyed

	has (v: like item): BOOLEAN
			-- Does structure include an occurrence of v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty

	has_recursively (an_item: like item): BOOLEAN
			-- Does Current contain an_item at any level?

	frozen id_object (an_id: INTEGER): IDENTIFIED
			-- Object associated with an_id (void if no such object)
			-- (from IDENTIFIED)
		ensure -- from IDENTIFIED
			consistent: Result = void or else Result.object_id = an_id

	index: INTEGER
			-- Index of current position
			-- (from LINEAR)

	index_of (v: like item; i: INTEGER): INTEGER
			-- Index of i-th occurrence of v.
			-- 0 if none.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from LINEAR
			positive_occurrences: i > 0
		ensure -- from LINEAR
			non_negative_result: Result >= 0

	item: EV_TREE_NODE
			-- Item at current position
			-- (from TRAVERSABLE)
		require -- from TRAVERSABLE
			not_off: not off

	frozen object_id: INTEGER
			-- Unique for current object in any given session
			-- (from IDENTIFIED)
		ensure -- from IDENTIFIED
			valid_id: id_object (Result) = Current

	occurrences (v: EV_TREE_NODE): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)

	parent: EV_TREE_NODE_CONTAINER
			-- Parent of Current.
		require
			not_destroyed: not is_destroyed

	parent_tree: EV_TREE
			-- Contains Current.
		require
			not_destroyed: not is_destroyed

	pebble: ANY
			-- Data to be transported by pick and drop mechanism.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.pebble

	pebble_function: FUNCTION [ANY, TUPLE, ANY]
			-- Returns data to be transported by pick and drop mechanism.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.pebble_function

	pebble_positioning_enabled: BOOLEAN
			-- If True then pick and drop start coordinates are
			-- pebble_x_position, pebble_y_position.
			-- If False then pick and drop start coordinates are
			-- the pointer coordinates.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.pebble_positioning_enabled

	pebble_x_position: INTEGER
			-- Initial x position for pick and drop relative to Current.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.pebble_x_position

	pebble_y_position: INTEGER
			-- Initial y position for pick and drop relative to Current.
			-- (from EV_PICK_AND_DROPABLE)
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.pebble_y_position

	pixmap: EV_PIXMAP
			-- Image displayed on Current.
			-- (from EV_PIXMAPABLE)
		require -- from EV_PIXMAPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PIXMAPABLE
			bridge_ok: (Result = void and implementation.pixmap = void) or Result.is_equal (implementation.pixmap)

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- If no such position ensure that exhausted will be true.
			-- (from LINEAR)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies equal (v, item)
			item_found: (not exhausted and not object_comparison) implies v = item

	target_name: STRING
			-- Optional textual name describing Current pick and drop hole.
			-- (from EV_ABSTRACT_PICK_AND_DROPABLE)

	text: STRING
			-- Text displayed in textable.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			bridge_ok: equal (Result, implementation.text)
			not_void_implies_cloned: Result /= void implies Result /= implementation.text

	tooltip: STRING
			-- Tooltip displayed on Current.
			-- (from EV_TOOLTIPABLE)
		require -- from EV_TOOLTIPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TOOLTIPABLE
			bridge_ok: (Result = void and implementation.tooltip = void) or Result.is_equal (implementation.tooltip)
	
feature -- Status report

	after: BOOLEAN
			-- Is there no valid position to the right of current one?
			-- (from LINEAR)

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)

	exhausted: BOOLEAN
			-- Has structure been completely explored?
			-- (from LINEAR)
		ensure -- from LINEAR
			exhausted_when_off: off implies Result

	is_empty: BOOLEAN
			-- Is there no element?
			-- (from CONTAINER)

	is_expanded: BOOLEAN
			-- Are items in Current displayed?
		require
			not_destroyed: not is_destroyed

	is_selectable: BOOLEAN
			-- May enable_select be called.
			-- (from EV_SELECTABLE)
		require -- from EV_SELECTABLE
			not_destroyed: not is_destroyed

	is_selected: BOOLEAN
			-- Is selected.
			-- (from EV_SELECTABLE)
		require -- from EV_SELECTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_SELECTABLE
			bridge_ok: Result = implementation.is_selected

	mode_is_drag_and_drop: BOOLEAN
			-- Is the user interface mode drag and drop?
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.mode_is_drag_and_drop

	mode_is_pick_and_drop: BOOLEAN
			-- Is the user interface mode pick and drop?
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.mode_is_pick_and_drop

	mode_is_target_menu: BOOLEAN
			-- Is the user interface mode a pop-up menu of targets?
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure then -- from EV_PICK_AND_DROPABLE
			bridge_ok: Result = implementation.mode_is_target_menu

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	off: BOOLEAN
			-- Is there no current item?
			-- (from LINEAR)
	
feature -- Status setting

	align_text_center
			-- Display text centered.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			alignment_set: alignment.is_center_aligned

	align_text_left
			-- Display text left aligned.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			alignment_set: alignment.is_left_aligned

	align_text_right
			-- Display text right aligned.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			alignment_set: alignment.is_right_aligned

	collapse
			-- Set is_expanded False.
		require
			not_destroyed: not is_destroyed
			parent_tree_not_void: parent_tree /= void
			is_collapsable: is_expandable
		ensure
			not_is_expanded: not is_expanded

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			object_comparison

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			reference_comparison: not object_comparison

	disable_pebble_positioning
			-- Assign False to pebble_positioning_enabled.
			-- The pick and drop will start at the pointer position.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			pebble_positioning_updated: not pebble_positioning_enabled

	disable_select
			-- Deselect the object.
			-- (from EV_DESELECTABLE)
		require -- from EV_DESELECTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_DESELECTABLE
			unselected: not is_selected

	enable_pebble_positioning
			-- Assign True to pebble_positioning_enabled.
			-- Use pebble_x_position and pebble_y_position as the initial coordinates
			-- for the pick and drop in pixels relative to Current.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			pebble_positioning_updated: pebble_positioning_enabled

	enable_select
			-- Make is_selected True.
			-- (from EV_SELECTABLE)
		require -- from EV_SELECTABLE
			not_destroyed: not is_destroyed
			is_selectable: is_selectable
		ensure -- from EV_SELECTABLE
			is_selected: is_selected

	expand
			-- Set is_expanded True.
		require
			not_destroyed: not is_destroyed
			parent_tree_not_void: parent_tree /= void
			is_expandable: is_expandable
		ensure
			is_expanded: is_expanded

	remove_pebble
			-- Make pebble Void and pebble_function `Void,
			-- Removing transport.
			-- (from EV_PICK_AND_DROPABLE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_removed: pebble = void and pebble_function = void

	set_accept_cursor (a_cursor: EV_CURSOR)
			-- Set a_cursor to be displayed when the screen pointer is over a
			-- target that accepts pebble during pick and drop.
			-- (from EV_PICK_AND_DROPABLE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			accept_cursor_assigned: accept_cursor.is_equal (a_cursor)

	set_deny_cursor (a_cursor: EV_CURSOR)
			-- Set a_cursor to be displayed when the screen pointer is not
			-- over a valid target.
			-- (from EV_PICK_AND_DROPABLE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			deny_cursor_assigned: deny_cursor.is_equal (a_cursor)

	set_drag_and_drop_mode
			-- Set user interface mode to drag and drop.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			drag_and_drop_set: mode_is_drag_and_drop

	set_pebble (a_pebble: like pebble)
			-- Assign a_pebble to pebble.
			-- Overrides set_pebble_function.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_pebble_not_void: a_pebble /= void
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_assigned: pebble = a_pebble

	set_pebble_function (a_function: FUNCTION [ANY, TUPLE, ANY])
			-- Set a_function to compute pebble.
			-- It will be called once each time a pick occurs, the result
			-- will be assigned to pebble for the duration of transport.
			-- When a pick occurs, the pick position in widget coordinates,
			-- <<x, y>> in pixels, is passed.
			-- To handle this data use a_function of type
			-- FUNCTION [ANY, TUPLE [INTEGER, INTEGER], ANY] and return the
			-- pebble as a function of x and y.
			-- Overrides set_pebble.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_function_not_void: a_function /= void
			a_function_takes_two_integer_open_operands: a_function.valid_operands ([1, 1])
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_function_assigned: pebble_function = a_function

	set_pebble_position (a_x, a_y: INTEGER)
			-- Set the initial position for pick and drop
			-- Coordinates are in pixels and are relative to position of Current.
			-- Pebble_positioning_enabled must be True for the position to be used,
			-- use enable_pebble_positioning.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			pebble_position_assigned: pebble_x_position = a_x and pebble_y_position = a_y

	set_pick_and_drop_mode
			-- Set user interface mode to pick and drop.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			pick_and_drop_set: mode_is_pick_and_drop

	set_target_menu_mode
			-- Set user interface mode to pop-up menu of targets.
			-- (from EV_PICK_AND_DROPABLE)
		require -- from EV_PICK_AND_DROPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PICK_AND_DROPABLE
			target_menu_mode_set: mode_is_target_menu

	set_target_name (a_name: STRING)
			-- Assign a_name to target_name.
			-- (from EV_ABSTRACT_PICK_AND_DROPABLE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_name_not_void: a_name /= void
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			target_name_assigned: a_name /= target_name and a_name.is_equal (target_name)

	toggle
			-- Change is_selected.
			-- (from EV_DESELECTABLE)
		require -- from EV_DESELECTABLE
			not_is_destroyed: not is_destroyed
			can_be_selected: not is_selected implies is_selectable
		ensure -- from EV_DESELECTABLE
			is_selected_changed: is_selected /= old is_selected
	
feature -- Cursor movement

	finish
			-- Move to last position.
			-- (from LINEAR)

	forth
			-- Move to next position; if no next position,
			-- ensure that exhausted will be true.
			-- (from LINEAR)
		require -- from LINEAR
			not_after: not after

	start
			-- Move to first position if any.
			-- (from TRAVERSABLE)
	
feature -- Element change

	remove_pixmap
			-- Make pixmap Void.
			-- (from EV_PIXMAPABLE)
		require -- from EV_PIXMAPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_PIXMAPABLE
			pixmap_removed: pixmap = void

	remove_text
			-- Make text Void.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TEXTABLE
			text_removed: text = void

	remove_tooltip
			-- Make tooltip Void.
			-- (from EV_TOOLTIPABLE)
		require -- from EV_TOOLTIPABLE
			not_destroyed: not is_destroyed
		ensure -- from EV_TOOLTIPABLE
			tooltip_removed: tooltip = void

	set_data (some_data: like data)
			-- Assign some_data to data.
			-- (from EV_ANY)
		require -- from EV_ANY
			not_destroyed: not is_destroyed
		ensure -- from EV_ANY
			data_assigned: data = some_data

	set_pixmap (a_pixmap: EV_PIXMAP)
			-- Assign a_pixmap to pixmap.
			-- (from EV_PIXMAPABLE)
		require -- from EV_PIXMAPABLE
			not_destroyed: not is_destroyed
			pixmap_not_void: a_pixmap /= void
		ensure -- from EV_PIXMAPABLE
			pixmap_assigned: a_pixmap.is_equal (pixmap) and pixmap /= a_pixmap

	set_text (a_text: STRING)
			-- Assign a_text to text.
			-- (from EV_TEXTABLE)
		require -- from EV_TEXTABLE
			not_destroyed: not is_destroyed
			a_text_not_void: a_text /= void
			a_text_not_empty: not a_text.is_empty
		ensure -- from EV_TEXTABLE
			text_cloned: text.is_equal (a_text) and then text /= a_text

	set_tooltip (a_tooltip: STRING)
			-- Assign a_tooltip to tooltip.
			-- (from EV_TOOLTIPABLE)
		require -- from EV_TOOLTIPABLE
			not_destroyed: not is_destroyed
			tooltip: a_tooltip /= void
			a_tooltip_not_empty: not a_tooltip.is_empty
		ensure -- from EV_TOOLTIPABLE
			tooltip_assigned: a_tooltip.is_equal (tooltip) and tooltip /= a_tooltip
	
feature -- Conversion

	linear_representation: LINEAR [EV_TREE_NODE]
			-- Representation as a linear structure
			-- (from LINEAR)
	
feature -- Duplication

	copy (other: like Current)
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from EV_ANY)
		require -- from ANY
			other_not_void: other /= void
			type_identity: same_type (other)
		ensure -- from ANY
			is_equal: is_equal (other)
	
feature -- Command

	destroy
			-- Destroy underlying native toolkit object.
			-- Render Current unusable.
			-- (from EV_ANY)
		ensure -- from EV_ANY
			is_destroyed: is_destroyed
	
feature -- Contract support

	is_expandable: BOOLEAN
			-- Can Current be expanded and collapsed?
		require
			not_destroyed: not is_destroyed
	
feature -- Event handling

	collapse_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when collapsed.
			-- (from EV_TREE_NODE_ACTION_SEQUENCES)
		ensure -- from EV_TREE_NODE_ACTION_SEQUENCES
			not_void: Result /= void

	conforming_pick_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when a pebble that fits here is picked.
			-- (from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES)
		ensure -- from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES
			not_void: Result /= void

	deselect_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when deselected.
			-- (from EV_TREE_NODE_ACTION_SEQUENCES)
		ensure -- from EV_TREE_NODE_ACTION_SEQUENCES
			not_void: Result /= void

	drop_actions: EV_PND_ACTION_SEQUENCE
			-- Actions to be performed when a pebble is dropped here.
			-- (from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES)
		ensure -- from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES
			not_void: Result /= void

	expand_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when expanded.
			-- (from EV_TREE_NODE_ACTION_SEQUENCES)
		ensure -- from EV_TREE_NODE_ACTION_SEQUENCES
			not_void: Result /= void

	pick_actions: EV_PND_START_ACTION_SEQUENCE
			-- Actions to be performed when pebble is picked up.
			-- (from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES)
		ensure -- from EV_PICK_AND_DROPABLE_ACTION_SEQUENCES
			not_void: Result /= void

	pointer_button_press_actions: EV_POINTER_BUTTON_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer button is pressed.
			-- (from EV_ITEM_ACTION_SEQUENCES)
		ensure -- from EV_ITEM_ACTION_SEQUENCES
			not_void: Result /= void

	pointer_double_press_actions: EV_POINTER_BUTTON_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer is double clicked.
			-- (from EV_ITEM_ACTION_SEQUENCES)
		ensure -- from EV_ITEM_ACTION_SEQUENCES
			not_void: Result /= void

	pointer_motion_actions: EV_POINTER_MOTION_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer moves.
			-- (from EV_ITEM_ACTION_SEQUENCES)
		ensure -- from EV_ITEM_ACTION_SEQUENCES
			not_void: Result /= void

	select_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when selected.
			-- (from EV_TREE_NODE_ACTION_SEQUENCES)
		ensure -- from EV_TREE_NODE_ACTION_SEQUENCES
			not_void: Result /= void
	
feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [EV_TREE_NODE]])
			-- Apply action to every item.
			-- Semantics not guaranteed if action changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void

	do_if (action: PROCEDURE [ANY, TUPLE [EV_TREE_NODE]]; test: FUNCTION [ANY, TUPLE [EV_TREE_NODE], BOOLEAN])
			-- Apply action to every item that satisfies test.
			-- Semantics not guaranteed if action or test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void
			test_exits: test /= void

	for_all (test: FUNCTION [ANY, TUPLE [EV_TREE_NODE], BOOLEAN]): BOOLEAN
			-- Is test true for all items?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

	there_exists (test: FUNCTION [ANY, TUPLE [EV_TREE_NODE], BOOLEAN]): BOOLEAN
			-- Is test true for at least one item?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void
	
feature -- Status Report

	is_destroyed: BOOLEAN
			-- Is Current no longer usable?
			-- (from EV_ANY)
		ensure -- from EV_ANY
			bridge_ok: Result = implementation.is_destroyed
	
invariant

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from EV_PICK_AND_DROPABLE
	user_interface_modes_mutually_exclusive: mode_is_pick_and_drop.to_integer + mode_is_drag_and_drop.to_integer + mode_is_target_menu.to_integer = 1
		-- from EV_ANY
	is_initialized: is_initialized
	is_coupled: implementation /= void and then implementation.interface = Current
	default_create_called: default_create_called
		-- from EV_TEXTABLE
	text_not_void_implies_text_not_empty: is_usable and text /= void implies text.count > 0
		-- from EV_DESELECTABLE
	not_selectable_therefore_not_selected: not is_selectable implies not is_selected
		-- from LINEAR
	after_constraint: after implies off
		-- from TRAVERSABLE
	empty_constraint: is_empty implies off

end -- class EV_TREE_NODE