Disowned A sheet is said to be disowned if it does not have a parent. A sheet ceases to be a
child of another sheet by being disowned.

Grafted A sheet is said to be grafted when it is part of a sheet hierarchy whose highest ancestor
is a graft. In this case, the sheet may be visible on a particular window server.

Degrafted A sheet is said to be degrafted when it is part of a sheet hierarchy that cannot
possibly be visible on a server, that is, the highest ancestor is not a graft.

Enabled A sheet is said to be enabled when it is actively participating in the windowing rela-
tionship with its parent. If a sheet is enabled and grafted, and all its ancestors are enabled
(they are grafted by definition), then the sheet will be visible if it occupies a portion of the
graft region that isn't clipped by its ancestors or ancestor's siblings.

Disabled The opposite of enabled is disabled.

7.2.1 Sheet Relationship Functions

The generic functions in this section comprise the sheet protocol. All sheet objects must imple-
ment or inherit methods for each of these generic functions.

=> sheet-parent sheet [Generic Function]
Returns the parent of the sheet sheet, or nil if the sheet has no parent.

=> sheet-children sheet [Generic Function]
Returns a list of sheets that are the children of the sheet sheet. Some sheet classes support only
a single child; in this case, the result of sheet-children will be a list of one element. This
function returns objects that reveal CLIM's internal state; do not modify those objects.

=> sheet-adopt-child sheet child [Generic Function]
Adds the child sheet child to the set of children of the sheet sheet, and makes the sheet the child's
parent. If child already has a parent, the sheet-already-has-parent error will be signalled.

Some sheet classes support only a single child. For such sheets, attempting to adopt more than
a single child will cause the sheet-supports-only-one-child error to be signalled.

=> sheet-disown-child sheet child &key (errorp t) [Generic Function]
Removes the child sheet child from the set of children of the sheet sheet, and makes the parent
of the child be nil. If child is not actually a child of sheet and errorp is true, then the sheet-
is-not-child error will be signalled.

=> sheet-siblings sheet [Generic Function]
Returns a list of all of the siblings of the sheet sheet. The sibling are all of the children of sheet's
parent excluding sheet itself. This function returns fresh objects that may be modified.

=> sheet-enabled-children sheet [Generic Function]