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A panel is a used as a temporary floating popup window that may contain any type of content. It does not have any window decorations. When open, it floats above the window and may extend outside the border of the main window. Typically, it will be attached to a button using the button's type attribute so that when the button is pressed, the panel will be displayed. A panel may also be opened via a script using the openPopup method.

The panel is closed when the user clicks outside the panel, presses Escape or when the panel's hidePopup method is called.

Warning: For Firefox versions between 3.6 and 4.0, placing an iframe, browser or editor inside a panel is not supported. Some features may work, but only on some platforms. For those versions of Firefox, it is best to avoid child frames in a panel, if possible. This limitation was resolved as of Firefox 4.0.
backdrag, close, consumeoutsideclicks, fade, flip, ignorekeys, label, left, levelnoautofocus, noautohide, norestorefocus, onpopuphidden, onpopuphiding, onpopupshowing, onpopupshown, position, titlebar, top, type
accessibleType, label, popupBoxObject, popup, state
hidePopup, moveTo, openPopup, openPopupAtScreen, sizeTo


The following example shows how a panel may be attached to a label.

<panel id="thepanel">
  <hbox align="start">
    <image src="warning.png"/>
      <description value="You have 6 new messages."/>
        <button label="Read Mail"/>
        <button label="New Message"/>
<description value="6 New Messages" popup="thepanel"/>


Type: boolean
Setting the backdrag attribute on a XUL panel lets the user move the panel by clicking and dragging anywhere on its background area.
Type: boolean
If the panel has a titlebar, set the panel's close attribute to true to have a close button appear on the titlebar. Pressing the close button will close the panel.
Type: boolean
Controls whether or not the event that caused the popup to be automatically dismissed (or "rolled up") should be consumed or be dispatched as a normal event. If it is not set, it defaults to the platform behavior. If it set to true the rollup event is consumed. If set to false, the rollup event is not consumed. This attribute should be used instead of setConsumeRollupEvent.
Type: one of the values below
The fade attribute, which may only be used with arrow panels, lets you set up a panel that will automatically fade away after a short time. The default is none.
The panels doesn't automatically fade away.
The panels slowly fades away after a short time.
The panels quickly fades away after a short time.
Type: string
Normally, when a popup opens near the edge of the screen, it flips over to open on the opposite side of the anchor, so that it doesn't extend off the screen. For example, if the menu doesn't have room to open downward, it flips to open upward instead; this is a vertical flip. Horizontal flipping doesn't normally happen, since this would cause menus to open in strange places. For arrow popups, however, being able to flip horizontally makes sense. This attribute, set to both, permits that behavior. You will not normally have to use this attribute, since it's automatically applied to arrow panels.
An arrow panel can also specify a value of slide, which causes the arrow to "slide" instead of flipping when the panel doesn't have room.  A sliding panel will have the start (or end) position extended such that the panel can be the requested size, meaning the arrow will no longer be at the start (or end) of the panel - i.e., the arrow will appear to have been slid along the panel to ensure the arrow is still pointing at the anchor.
Panel with flip="slide"
In this image, the panel has flip="slide" and has a width which is greater than the distance from the anchor to the right of the screen (or window), so the panel extends past the left of the anchor, and the arrow slides towards the middle of the panel such that it is still aligned with the anchor.  Without flip="slide", the panel would have had its width truncated and the panel would not extend to the left of the anchor.
Type: boolean
If false, the default value, the Escape key may be used to close the panel. If true, the Escape key cannot be used to close the panel.
Type: string
For panels with titlebars, the label on the titlebar.
Type: integer
Overrides the horizontal position of the popup specified by the showPopup method.
Type: one of the values below
Specifies whether the panel appears on top of all windows, or just on top of the window the panel is in. If this attribute is not set, the popup window level depends on the platform. On Linux, the default value is top, otherwise, the default value is parent. If a panel has one or more text fields, this attribute should not be set, otherwise IME or on-screen keyboard popups will appear incorrectly. For these reasons, you should avoid setting the level if not needed.
The panel is shown in front of all other normal windows, including those of other applications.
The panel is shown just above the window the panel is in, but behind other windows above it. If anchored, the child window maintains its relative position to its parent window.
The panel floats above the window the panel is in. On Mac, the panel is only visible when the application is active.
Type: boolean
If false, the default value, the currently focused element will be unfocused whenever the popup is opened or closed. If true, the focus is not adjusted.
Type: boolean
If false, the default value, the panel will be hidden when the user clicks outside the panel or switches focus to another application. If true, the panel will only be closed when the hidePopup method is called.
Type: boolean
If false, the default value, then when the panel is hidden, the keyboard focus will be restored to whatever had the focus before the panel was opened. If true, the focus will not be reset, although it will be cleared if the focus is within the panel.
Type: script code
This event is sent to a popup after it has been hidden.
This event may also be received while the popup is still open, but when sub-menus contained within this popup are hidden.


<menupopup id="top" onpopuphidden="console.log('The onpopuphidden method of id=top was called.');">
    <menuitem label="item 1"/>
    <menuitem label="item 2"/>
    <menu id="submenu1" label="submenu 1">
        <menupopup id="submenu1-popup">
            <menuitem label="submenu1 item 1"/>
            <menuitem label="submenu1 item 2"/>
    <menu id="submenu2" label="submenu 1">
        <menupopup id="submenu2-popup">
            <menuitem label="submenu2 item 1"/>
            <menuitem label="submenu2 item 2"/>
Type: script code
This event is sent to a popup when it is about to be hidden.
Type: script code
This event is sent to a popup just before it is opened. This handler is usually used to dynamically set the contents when the user requests to display it. Returning false from this event handler prevents the popup from appearing.
Type: script code
This event is sent to a popup after it has been opened, much like the onload event is sent to a window when it is opened.
Type: string
The position attribute determines where the popup appears relative to the element the user clicked to invoke the popup. This allows you to place the popup on one side of a button.  Note that a context menu will never respect this attribute, always appearing relative to the mouse cursor.

This value can be specified either as a single word offering pre-defined alignment positions, or as 2 words specifying exactly which part of the anchor and popup should be aligned.

If specified as 2 words, the value indicates which corner or edge of the anchor (the first word) is aligned which which corner of the popup (the second word).  The anchor value (ie, the first word) can be one of topleft, topright, bottomleft, bottomright, leftcenter, rightcenter, topcenter or bottomcenter.  The popup value (ie, the second word) can be one of topleft, topright, bottomleft or bottomright.

Positions specified as a single word string are shortcuts for the values above.  Valid single-word values are after_start, after_end, before_start, before_end, end_after, end_before, start_after, start_before, overlap, at_pointer or after_pointer.
For more details, including examples, please see popup positioning
Type: string
Set the panel's titlebar attribute to the value normal to display a panel with a titlebar. The noautohide attribute must be set to true.
Type: integer
Overrides the vertical position of the popup specified by the showPopup method.
Type: string
The panel type. Should be one of the following:
Specify this for a panel that provides a tree for an autocomplete element.
Specify this for a panel that provides a richlistbox for an autocomplete element.
Specify this for a panel that provides an arrow pointing at its anchor.
Specify this for a panel that's being used as a drag image for a drag and drop operation.
Otherwise leave this attribute out.
Note: The arrow will draw as long as the panel doesn't overlap the anchor. If they overlap, the anchor won't be drawn. The panel may not appear on the side of the anchor that you requested in which case the arrow will automatically adjust.


Type: integer
A value indicating the type of accessibility object for the element.
Type: string
Gets and sets the value of the label attribute.
Type: nsIPopupBoxObject
This read-only property holds the nsIPopupBoxObject that implements the popup. You wouldn't normally need to use this property as all of its functions are available via the popup itself.
Type: string
Gets and sets the value of the position attribute.
Type: string
This read only property indicates whether the popup is open or not. Four values are possible:
  • closed: The popup is closed and not visible.
  • open: The popup is open and visible on screen.
  • showing: A request has been made to open the popup, but it has not yet been shown. This state will occur during the popupshowing event.
  • hiding: The popup is about to be hidden. This state will occur during the popuphiding event.


Inherited Methods
addEventListener(), appendChild(), blur, click, cloneNode(), compareDocumentPosition, dispatchEvent(), doCommand, focus, getAttribute(), getAttributeNode(), getAttributeNodeNS(), getAttributeNS(), getBoundingClientRect(), getClientRects(), getElementsByAttribute, getElementsByAttributeNS, getElementsByClassName(), getElementsByTagName(), getElementsByTagNameNS(), getFeature(), getUserData, hasAttribute(), hasAttributeNS(), hasAttributes(), hasChildNodes(), insertBefore(), isDefaultNamespace(), isEqualNode, isSameNode, isSupported(), lookupNamespaceURI, lookupPrefix, normalize(), querySelector(), querySelectorAll(), removeAttribute(), removeAttributeNode(), removeAttributeNS(), removeChild(), removeEventListener(), replaceChild(), setAttribute(), setAttributeNode(), setAttributeNodeNS(), setAttributeNS(), setUserData

Return type: no return value
Closes the popup immediately.
moveTo( x, y )
Return type: no return value
Moves the popup to a new location defined by screen coordinates (and not client coordinates).
If both x and y have the value -1 the call will realign the popup with its anchor node.
openPopup( anchor , position , x , y , isContextMenu, attributesOverride, triggerEvent )
Return type: no return value

Opens the popup relative to a specified node at a specific location.

The popup may be either anchored to another node or opened freely. To anchor a popup to a node, supply an anchor node and set the position to a string indicating the manner in which the popup should be anchored. The anchor node does not need to be in the same document as the popup. Unanchored popups may be created by supplying null as the anchor node. The direction in which the popup is oriented depends on the direction of the anchor.
Possible values for position are: before_start, before_end, after_start, after_end, start_before, start_after, end_before, end_after, overlap, and after_pointer. Check Positioning of the Popup Guide for a precise description of the effect of the different values.
x, y
For an anchored popup, the x and y arguments may be used to offset the popup from its anchored position by some number, measured in CSS pixels. An unanchored popup appears at the position specified by x and y, relative to the viewport of the document containing the popup node. In this case, the position and attributesOverride arguments are ignored.
The isContextMenu argument should be true for context menus and false for all other types of popups. It affects menu item highlighting; that is, while a context menu is open, menus opened earlier do not highlight or execute their items.
If the attributesOverride argument is true, the position attribute on the popup node overrides the position value argument. If attributesOverride is false, the attribute is only used if the position argument is empty.
The event that triggered the popup (such as a mouse click, if the user clicked something to open the popup).
openPopupAtScreen( x, y, isContextMenu )
Return type: no return value
Open the popup at a specific screen position specified by x and y. This position may be adjusted if it would cause the popup to be off of the screen. The x and y coordinates are measured in CSS pixels.
sizeTo( width, height )
Return type: no return value
Changes the current size of the popup to the new width and height.
nsIAccessibleProvider, nsIDOMXULPopupElement