nsITreeView Interface

 Methods used by the drag feedback code to determine if a drag is allowable at
 the current location. To get the behavior where drops are only allowed on
 items, such as the mailNews folder pane, always return false when
 the orientation is not DROP_ON.

boolean canDrop(in long index, in long orientation)

 Called on the view when a cell in a non-selectable cycling column (e.g., unread/flag/etc.) is clicked.

void cycleCell(in long row, in nsITreeColumn col)

 Called on the view when a header is clicked.

void cycleHeader(in nsITreeColumn col)

 Called when the user drops something on this view. The |orientation| param
 specifies before/on/after the given |row|.

void drop(in long row, in long orientation)

 An atomized list of properties for a given cell.  Each property, x, that
 the view gives back will cause the pseudoclass :moz-tree-cell-x
 to be matched on the ::moz-tree-cell pseudoelement.

void getCellProperties(in long row, in nsITreeColumn col, in nsISupportsArray properties)

 The text for a given cell.  If a column consists only of an image, then
 the empty string is returned.  

AString getCellText(in long row, in nsITreeColumn col)

 The value for a given cell. This method is only called for columns
 of type other than |text|.

AString getCellValue(in long row, in nsITreeColumn col)

 Called to get properties to paint a column background.  For shading the sort
 column, etc.

void getColumnProperties(in nsITreeColumn col, in nsISupportsArray properties)

 The image path for a given cell. For defining an icon for a cell.
 If the empty string is returned, the :moz-tree-image pseudoelement
 will be used.

AString getImageSrc(in long row, in nsITreeColumn col)

 The level is an integer value that represents
 the level of indentation.  It is multiplied by the width specified in the 
 :moz-tree-indentation pseudoelement to compute the exact indendation.

long getLevel(in long index)

 Methods used by the tree to draw thread lines in the tree.
 getParentIndex is used to obtain the index of a parent row.
 If there is no parent row, getParentIndex returns -1.

long getParentIndex(in long rowIndex)

 
 An atomized list of properties for a given row.  Each property, x, that
 the view gives back will cause the pseudoclass :moz-tree-row-x
 to be matched on the pseudoelement ::moz-tree-row.

void getRowProperties(in long index, in nsISupportsArray properties)

 hasNextSibling is used to determine if the row at rowIndex has a nextSibling
 that occurs *after* the index specified by afterIndex.  Code that is forced
 to march down the view looking at levels can optimize the march by starting
 at afterIndex+1.

boolean hasNextSibling(in long rowIndex, in long afterIndex)

 Methods that can be used to test whether or not a twisty should be drawn,
 and if so, whether an open or closed twisty should be used.

boolean isContainer(in long index)

 isEditable is called to ask the view if the cell contents are editable.
 A value of true will result in the tree popping up a text field when 
 the user tries to inline edit the cell.

boolean isEditable(in long row, in nsITreeColumn col)

 isSeparator is used to determine if the row at index is a separator.
 A value of true will result in the tree drawing a horizontal separator.
 The tree uses the ::moz-tree-separator pseudoclass to draw the separator.

boolean isSeparator(in long index)

 Specifies if there is currently a sort on any column. Used mostly by dragdrop
 to affect drop feedback.

boolean isSorted()

 A command API that can be used to invoke commands on the selection.  The tree
 will automatically invoke this method when certain keys are pressed.  For example,
 when the DEL key is pressed, performAction will be called with the "delete" string.

void performAction(in wstring action)

 A command API that can be used to invoke commands on a specific cell.

void performActionOnCell(in wstring action, in long row, in nsITreeColumn col)

 A command API that can be used to invoke commands on a specific row.

void performActionOnRow(in wstring action, in long row)

 Should be called from a XUL onselect handler whenever the selection changes.

void selectionChanged()

 setCellText is called when the contents of the cell have been edited by the user.

void setCellText(in long row, in nsITreeColumn col, in AString value)

 setCellValue is called when the value of the cell has been set by the user.
 This method is only called for columns of type other than |text|.

void setCellValue(in long row, in nsITreeColumn col, in AString value)

 Called during initialization to link the view to the front end box object.

void setTree(in nsITreeBoxObject tree)

 Called on the view when an item is opened or closed.

void toggleOpenState(in long index)