<?xml version="1.0"?>

    <!-- See UiBinder.xsd for some XML Schema tips. -->

<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="urn:import:com.google.gwt.user.client.ui"
    xmlns="urn:import:com.google.gwt.user.client.ui"
    elementFormDefault="qualified">

    <xs:complexType
        name="CellPanelType">

        <!-- Any ordering, any number of occurrences -->
        <xs:choice
            minOccurs="0"
            maxOccurs="unbounded">

            <!-- The "cell" child -->
            <xs:element
                name="cell">
                <xs:complexType>

                    <!-- Require one widget -->
                    <xs:sequence>
                        <xs:any
                            processContents="lax" />
                    </xs:sequence>

                    <xs:attribute
                        name="horizontalAlignment"
                        type="xs:string" />
                    <xs:attribute
                        name="verticalAlignment"
                        type="xs:string" />
                    <xs:attribute
                        name="width"
                        type="xs:string" />
                    <xs:attribute
                        name="height"
                        type="xs:string" />

                    <xs:anyAttribute
                        processContents="lax" />
                </xs:complexType>
            </xs:element>

            <!-- Any widget -->
            <xs:any
                processContents="lax" />

        </xs:choice>
        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <xs:element
        name="DockPanel"
        type="CellPanelType" />

    <xs:element
        name="HorizontalPanel"
        type="CellPanelType" />

    <xs:element
        name="VerticalPanel"
        type="CellPanelType" />

    <!-- CustomButton extends ButtonBase which implements HasHTML -->
    <xs:complexType
        name="CustomButtonType"
        mixed="true">
        <xs:all
            minOccurs="0"
            maxOccurs="1">
            <xs:element
                name="upFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
            <xs:element
                name="downFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
            <xs:element
                name="upHoveringFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
            <xs:element
                name="downHoveringFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
            <xs:element
                name="upDisabledFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
            <xs:element
                name="downDisabledFace"
                type="CustomButtonChildElement"
                minOccurs="0" />
        </xs:all>
        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <!-- Allow mixed content (text and elements) -->
    <xs:complexType
        name="CustomButtonChildElement"
        mixed="true">

        <!--  Allow any children (HTML elements) -->
        <xs:choice
            minOccurs="0"
            maxOccurs="unbounded">
            <xs:any
                processContents="lax" />
        </xs:choice>

        <xs:attribute
            name="image"
            type="xs:string" />

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <xs:element
        name="PushButton"
        type="CustomButtonType" />

    <xs:element
        name="ToggleButton"
        type="CustomButtonType" />

    <!--
        TODO: AFAICT, we cannot properly express the constraints of
        DisclosurePanel. These constraints are that the header is optional and
        any number of widgets are optional (and ordering is not enforced). Only
        one of "header" or "customHeader" can appear. Ideally, this would be
        something like <all><choice of header><choice minOccurs=0
        maxOccurs=unbounded><any /></choice></all>, but nesting <choice> inside
        <all> is not possible, nor is having a <any /> appear in <all>. It is
        currently not that important since we do not use this for validation.
    -->
    <xs:element
        name="DisclosurePanel">
        <xs:complexType>

            <!--
                Allow any number of these (this allows multiple headers, which
                is inconsistent with the actual parser logic, but we cannot
                express the true constraints in an XSD.)
            -->
            <xs:choice
                maxOccurs="unbounded"
                minOccurs="0">

                <xs:element
                    name="header">

                    <!-- Allow mixed content -->
                    <xs:complexType
                        mixed="true">

                        <!--  Allow any children (HTML elements) -->
                        <xs:choice
                            minOccurs="0"
                            maxOccurs="unbounded">
                            <xs:any
                                processContents="lax" />
                        </xs:choice>

                        <xs:attribute
                            name="openImage"
                            type="xs:string" />
                        <xs:attribute
                            name="closedImage"
                            type="xs:string" />

                        <xs:anyAttribute
                            processContents="lax" />
                    </xs:complexType>
                </xs:element>

                <xs:element
                    name="customHeader">
                    <xs:complexType>

                        <!-- Require one widget -->
                        <xs:sequence>
                            <xs:any
                                processContents="lax" />
                        </xs:sequence>

                        <xs:anyAttribute
                            processContents="lax" />
                    </xs:complexType>
                </xs:element>

                <!-- Allow any widget(s) -->
                <xs:any
                    processContents="lax" />

            </xs:choice>
            <xs:anyAttribute
                processContents="lax" />
        </xs:complexType>
    </xs:element>

    <xs:complexType
        name="DockLayoutPanelType">

        <!--
            Allow any number of occurrences of child elements ("center" can only
            really occur once, which this schema does not enforce.)
        -->
        <xs:choice
            maxOccurs="unbounded"
            minOccurs="0">
            <xs:element
                name="north"
                type="DockDirectionType">
            </xs:element>
            <xs:element
                name="south"
                type="DockDirectionType">
            </xs:element>
            <xs:element
                name="west"
                type="DockDirectionType">
            </xs:element>
            <xs:element
                name="east"
                type="DockDirectionType">
            </xs:element>
            <xs:element
                name="lineStart"
                type="DockDirectionType">
            </xs:element>
            <xs:element
                name="lineEnd"
                type="DockDirectionType">
            </xs:element>
            <!-- The center element does not require the size, only a widget -->
            <xs:element
                name="center"
                type="SingleChildWidgetType">
            </xs:element>
        </xs:choice>

        <xs:attribute
            name="unit"
            type="xs:string">
        </xs:attribute>

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <!-- Used for north, south, west, east, lineStart, and lineEnd in the DockLayoutPanel. -->
    <xs:complexType
        name="DockDirectionType">
        <xs:complexContent>
            <xs:extension
                base="SingleChildWidgetType">
                <xs:attribute
                    name="size"
                    type="xs:string"
                    use="required" />
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>

    <xs:complexType
        name="SingleChildWidgetType">

        <!-- Require one widget -->
        <xs:sequence>
            <xs:any
                processContents="lax" />
        </xs:sequence>

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <xs:element
        name="DockLayoutPanel"
        type="DockLayoutPanelType" />

    <xs:element
        name="SplitLayoutPanel"
        type="DockLayoutPanelType" />

    <xs:element
        name="HTMLPanel">

        <!-- Allow mixed content -->
        <xs:complexType
            mixed="true">

            <!--  Allow any children (HTML elements) -->
            <xs:choice
                minOccurs="0"
                maxOccurs="unbounded">
                <xs:any
                    processContents="lax" />
            </xs:choice>

            <xs:attribute
                name="tag"
                type="xs:string" />

            <xs:anyAttribute
                processContents="lax" />
        </xs:complexType>
    </xs:element>

    <xs:element
        name="LayoutPanel">
        <xs:complexType>

            <!-- Allow any number of "layer" children -->
            <xs:choice
                minOccurs="0"
                maxOccurs="unbounded">
                <xs:element
                    name="layer"
                    type="LayoutPanelLayer">
                </xs:element>
            </xs:choice>

            <xs:anyAttribute
                processContents="lax" />

        </xs:complexType>
    </xs:element>

    <xs:complexType
        name="LayoutPanelLayer">
        <xs:complexContent>
            <!-- Each "layer" element contains one child widget -->
            <xs:extension
                base="SingleChildWidgetType">

                <!--
                    ...and can contain any of these attributes. We do not
                    express the pair constraints here.
                -->
                <xs:attribute
                    name="left"
                    type="xs:string" />

                <xs:attribute
                    name="right"
                    type="xs:string" />

                <xs:attribute
                    name="width"
                    type="xs:string" />

                <xs:attribute
                    name="top"
                    type="xs:string" />

                <xs:attribute
                    name="bottom"
                    type="xs:string" />

                <xs:attribute
                    name="height"
                    type="xs:string" />

            </xs:extension>
        </xs:complexContent>
    </xs:complexType>

    <xs:complexType
        name="MenuBarType">

        <!-- Allow any number of "MenuItem" children -->
        <xs:choice
            minOccurs="0"
            maxOccurs="unbounded">
            <xs:element
                name="MenuItem">
                <!-- MenuItem implements HasHTML -->
                <xs:complexType
                    mixed="true">

                    <xs:choice
                        minOccurs="0"
                        maxOccurs="unbounded">
                        <xs:element
                            name="MenuBar"
                            type="MenuBarType" />
                        <xs:any
                            processContents="lax" />
                    </xs:choice>

                    <xs:anyAttribute
                        processContents="lax" />
                </xs:complexType>
            </xs:element>
        </xs:choice>

        <xs:attribute
            name="vertical"
            type="xs:string" />

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <xs:element
        name="MenuBar"
        type="MenuBarType" />


    <xs:element
        name="RadioButton">
        <!-- RadioButton extends ButtonBase which HasHTML -->
        <xs:complexType
            mixed="true">

            <xs:choice
                minOccurs="0"
                maxOccurs="unbounded">
                <xs:any
                    processContents="lax" />
            </xs:choice>

            <xs:attribute
                name="name"
                type="xs:string" />

            <xs:anyAttribute
                processContents="lax" />
        </xs:complexType>
    </xs:element>

    <xs:element
        name="StackLayoutPanel">
        <xs:complexType>

            <!-- Allow any number of "stack" children -->
            <xs:choice
                minOccurs="0"
                maxOccurs="unbounded">
                <xs:element
                    name="stack"
                    type="StackLayoutPanelStack">
                </xs:element>
            </xs:choice>

            <xs:attribute
                name="unit"
                type="xs:string" />

            <xs:anyAttribute
                processContents="lax" />
        </xs:complexType>
    </xs:element>

    <xs:complexType
        name="StackLayoutPanelStack">

        <!--
            The constraints we want are one header and one widget in any order.
            I don't think we can easily express this in XSD, so we do a closer
            approximation of requiring at least two from {header, custom header,
            or widget} (this violates the constraints in that two headers would
            be valid.)
        -->
        <xs:choice
            minOccurs="2"
            maxOccurs="unbounded">

            <xs:element
                name="header"
                type="MixedContentType" />

            <xs:element
                name="customHeader">
                <xs:complexType>

                    <!-- Require one widget in the custom header -->
                    <xs:sequence>
                        <xs:any
                            processContents="lax" />
                    </xs:sequence>

                    <xs:attribute
                        name="size"
                        type="xs:string" />

                    <xs:anyAttribute
                        processContents="lax" />
                </xs:complexType>
            </xs:element>

            <!-- Require one widget in the stack -->
            <xs:any
                processContents="lax" />

        </xs:choice>
        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <xs:element
        name="TabLayoutPanel">
        <xs:complexType>

            <!-- Any number of tabs -->
            <xs:choice
                minOccurs="0"
                maxOccurs="unbounded">

                <xs:element
                    name="tab">
                    <xs:complexType>

                        <!--
                            Another instance of our inability to express the
                            constraints. We require one body (a widget) and
                            optionally one of the two headers. Instead, this
                            schema allows any number of these.
                        -->
                        <xs:choice
                            minOccurs="0"
                            maxOccurs="unbounded">

                            <xs:element
                                name="header"
                                type="MixedContentType">
                            </xs:element>

                            <xs:element
                                name="customHeader"
                                type="SingleChildWidgetType" />

                            <!-- One widget -->
                            <xs:any
                                processContents="lax" />

                        </xs:choice>

                        <xs:anyAttribute
                            processContents="lax" />
                    </xs:complexType>
                </xs:element>
            </xs:choice>

            <xs:attribute
                name="barHeight"
                type="xs:string"
                use="required" />

            <xs:attribute
                name="barUnit"
                type="xs:string" />

            <xs:anyAttribute
                processContents="lax" />
        </xs:complexType>
    </xs:element>

    <!--
        A complex type that contains both text and elements. There is no schema
        for the elements, they can be any elements.
    -->
    <xs:complexType
        name="MixedContentType"
        mixed="true">

        <xs:choice
            minOccurs="0"
            maxOccurs="unbounded">
            <xs:any
                processContents="lax" />
        </xs:choice>

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <!--
        A complex type that contains only elements. There is no schema for the
        elements, they can be any elements.
    -->
    <xs:complexType
        name="ElementContentType">

        <xs:choice
            minOccurs="0"
            maxOccurs="unbounded">
            <xs:any
                processContents="lax" />
        </xs:choice>

        <xs:anyAttribute
            processContents="lax" />
    </xs:complexType>

    <!--
        Below are widgets that do not have a custom parser, but that implement
        the HasHTML interface. We must list these in the schema to allow Eclipse
        to show autocomplete proposals in the element's text content (e.g. a
        proposal for <ui:msg>)
    -->
    <xs:element
        name="Anchor"
        type="MixedContentType" />
    <xs:element
        name="Button"
        type="MixedContentType" />
    <xs:element
        name="CheckBox"
        type="MixedContentType" />
    <xs:element
        name="DialogBox"
        type="MixedContentType" />
    <xs:element
        name="HTML"
        type="MixedContentType" />
    <xs:element
        name="InlineHTML"
        type="MixedContentType" />
    <xs:element
        name="Hyperlink"
        type="MixedContentType" />
    <xs:element
        name="InlineHyperlink"
        type="MixedContentType" />
    <xs:element
        name="RichTextArea"
        type="MixedContentType" />
    <xs:element
        name="TreeItem"
        type="MixedContentType" />

    <!--
        Below are widgets that do not have a custom parser, but that implement
        the HasWidgets interface. We must list these in the schema to allow
        Eclipse to show autocomplete proposals for children of these elements.
    -->
    <xs:element
        name="CaptionPanel"
        type="ElementContentType" />
    <xs:element
        name="AbsolutePanel"
        type="ElementContentType" />
    <xs:element
        name="RootPanel"
        type="ElementContentType" />
    <xs:element
        name="DeckPanel"
        type="ElementContentType" />
    <xs:element
        name="FlowPanel"
        type="ElementContentType" />
    <xs:element
        name="LayoutPanel"
        type="ElementContentType" />
    <xs:element
        name="RootLayoutPanel"
        type="ElementContentType" />
    <xs:element
        name="StackPanel"
        type="ElementContentType" />
    <xs:element
        name="DecoratedStackPanel"
        type="ElementContentType" />
    <xs:element
        name="FlexTable"
        type="ElementContentType" />
    <xs:element
        name="Grid"
        type="ElementContentType" />
    <xs:element
        name="SimplePanel"
        type="ElementContentType" />
    <xs:element
        name="DecoratorPanel"
        type="ElementContentType" />
    <xs:element
        name="FocusPanel"
        type="ElementContentType" />
    <xs:element
        name="FormPanel"
        type="ElementContentType" />
    <xs:element
        name="PopupPanel"
        type="ElementContentType" />
    <xs:element
        name="DecoratedPopupPanel"
        type="ElementContentType" />
    <xs:element
        name="ScrollPanel"
        type="ElementContentType" />
    <xs:element
        name="HorizontalSplitPanel"
        type="ElementContentType" />
    <xs:element
        name="VerticalSplitPanel"
        type="ElementContentType" />
    <xs:element
        name="TabPanel"
        type="ElementContentType" />
    <xs:element
        name="DecoratedTabPanel"
        type="ElementContentType" />
    <xs:element
        name="Tree"
        type="ElementContentType" />

</xs:schema>