Builtin Elements#

Common properties#

Geometry#

These properties are valid on all visible items:

  • width and height (in length): The size of the element. When set, this overrides the default size.

  • x and y (in length): The position of the element relative to its parent.

  • z (in float): Allows to specify a different order to stack the items with its siblings. (default value: 0)

  • absolute-position (in Point): The position of the element within the contained window.

Layout#

These properties are valid on all visible items and can be used to specify constraints when used in layouts:

  • col, row, colspan, rowspan (in int): See GridLayout.

  • horizontal-stretch and vertical-stretch (in-out float): Specify how much relative space these elements are stretching in a layout. When 0, this means that the elements won’t be stretched unless all elements are 0. Builtin widgets have a value of either 0 or 1.

  • max-width and max-height (in length): The maximum size of an element

  • min-width and min-height (in length): The minimum size of an element

  • preferred-width and preferred-height (in length): The preferred size of an element

Miscellaneous#

  • cache-rendering-hint (in bool): When set to true, this provides a hint to the renderer to cache the contents of the element and all the children into an intermediate cached layer. For complex sub-trees that rarely change this may speed up the rendering, at the expense of increased memory consumption. Not all rendering backends support this, so this is merely a hint. (default value: false)

  • dialog-button-role (in enum DialogButtonRole): Specify that this is a button in a Dialog.

  • opacity (in float): A value between 0 and 1 (or a percentage) that is used to draw the element and its children with transparency. 0 is fully transparent (invisible), and 1 is fully opaque. The opacity is applied to the tree of child elements as if they were first drawn into an intermediate layer, and then the whole layer is rendered with this opacity. (default value: 1)

  • visible (in bool): When set to false, the element and all his children won’t be drawn and not react to mouse input (default value: true)

The following example demonstrates the opacity property with children. An opacity is applied to the red rectangle. Since the green rectangle is a child of the red one, you can see the gradient underneath it, but you can’t see the red rectangle through the green one.

export component Example inherits Window {
    width: 100px;
    height: 100px;
    background: @radial-gradient(circle, black, white, black, white);
    Rectangle {
        opacity: 0.5;
        background: red;
        border-color: #822;
        border-width: 5px;
        width: 50px; height: 50px;
        x: 10px; y: 10px;
        Rectangle {
            background: green;
            border-color: #050;
            border-width: 5px;
            width: 50px; height: 50px;
            x: 25px; y: 25px;
        }
    }
}

Accessibility#

Use the following accessible- properties to make your items interact well with software like screen readers, braille terminals and other software to make your application accessible.

  • accessible-role (in enum AccessibleRole): The role of the element. This property is mandatory to be able to use any other accessible properties. It should be set to a constant value. (default value: none for most elements, but text for the Text element)

  • accessible-checkable (in bool): Whether the element is can be checked or not.

  • accessible-checked (in bool): Whether the element is checked or not. This maps to the “checked” state of checkboxes, radio buttons, and other widgets.

  • accessible-description (in string): The description for the current element.

  • accessible-has-focus (in bool): Set to true when the current element currently has the focus.

  • accessible-label (in string): The label for an interactive element. (default value: empty for most elements, or the value of the text property for Text elements)

  • accessible-value-maximum (in float): The maximum value of the item. This is used for example by spin boxes.

  • accessible-value-minimum (in float): The minimum value of the item.

  • accessible-value-step (in float) The smallest increment or decrement by which the current value can change. This corresponds to the step by which a handle on a slider can be dragged.

  • accessible-value (in string): The current value of the item.

Drop Shadows#

To achieve the graphical effect of a visually elevated shape that shows a shadow effect underneath the frame of an element, it’s possible to set the following drop-shadow properties:

  • drop-shadow-blur (in length): The radius of the shadow that also describes the level of blur applied to the shadow. Negative values are ignored and zero means no blur. (default value: 0)

  • drop-shadow-color (in color): The base color of the shadow to use. Typically that color is the starting color of a gradient that fades into transparency.

  • drop-shadow-offset-x and drop-shadow-offset-y (in length): The horizontal and vertical distance of the shadow from the element’s frame. A negative value places the shadow left / above of the element.

The drop-shadow effect is supported for Rectangle elements.

Dialog#

Dialog is like a window, but it has buttons that are automatically laid out.

A Dialog should have one main element as child, that isn’t a button. The dialog can have any number of StandardButton widgets or other buttons with the dialog-button-role property. The buttons will be placed in an order that depends on the target platform at run-time.

The kind property of the StandardButtons and the dialog-button-role properties need to be set to a constant value, it can’t be an arbitrary variable expression. There can’t be several StandardButtons of the same kind.

A callback <kind>_clicked is automatically added for each StandardButton which doesn’t have an explicit callback handler, so it can be handled from the native code: For example if there is a button of kind cancel, a cancel_clicked callback will be added.

Properties#

  • icon (in image): The window icon shown in the title bar or the task bar on window managers supporting it.

  • title (in string): The window title that is shown in the title bar.

Example#

import { StandardButton, Button } from "std-widgets.slint";
export component Example inherits Dialog {
    Text {
      text: "This is a dialog box";
    }
    StandardButton { kind: ok; }
    StandardButton { kind: cancel; }
    Button {
      text: "More Info";
      dialog-button-role: action;
    }
}

Flickable#

The Flickable is a low-level element that is the base for scrollable widgets, such as the ScrollView. When the viewport-width or the viewport-height is greater than the parent’s width or height respectively, the element becomes scrollable. Note that the Flickable doesn’t create a scrollbar. When unset, the viewport-width and viewport-height are calculated automatically based on the Flickable’s children. This isn’t the case when using a for loop to populate the elements. This is a bug tracked in issue #407. The maximum and preferred size of the Flickable are based on the viewport.

When not part of a layout, its width or height defaults to 100% of the parent element when not specified.

Properties#

  • interactive (in bool): When true, the viewport can be scrolled by clicking on it and dragging it with the cursor. (default value: true)

  • viewport-height, viewport-width (in length): The total size of the scrollable element.

  • viewport-x, viewport-y (in length): The position of the scrollable element relative to the Flickable. This is usually a negative value.

Example#

export component Example inherits Window {
    width: 270px;
    height: 100px;

    Flickable {
        viewport-height: 300px;
        Text {
            x:0;
            y: 150px;
            text: "This is some text that you have to scroll to see";
        }
    }
}

FocusScope#

The FocusScope exposes callbacks to intercept key events. Note that FocusScope will only invoke them when it has-focus.

The KeyEvent has a text property, which is a character of the key entered. When a non-printable key is pressed, the character will be either a control character, or it will be mapped to a private unicode character. The mapping of these non-printable, special characters is available in the Key namespace

Properties#

  • has-focus (out bool): Is true when the element has keyboard focus.

  • enabled (in bool): When true, the FocusScope will make itself the focused element when clicked. Set this to false if you don’t want the click-to-focus behavior. Similarly, a disabled FocusScope does not accept the focus via tab focus traversal. A parent FocusScope will still receive key events from child FocusScopes that were rejected, even if enabled is set to false. (default value: true)

Functions#

  • focus() Call this function to transfer keyboard focus to this FocusScope, to receive future KeyEvents.

Callbacks#

Example#

export component Example inherits Window {
    width: 100px;
    height: 100px;
    forward-focus: my-key-handler;
    my-key-handler := FocusScope {
        key-pressed(event) => {
            debug(event.text);
            if (event.modifiers.control) {
                debug("control was pressed during this event");
            }
            if (event.text == Key.Escape) {
                debug("Esc key was pressed")
            }
            accept
        }
    }
}

GridLayout#

GridLayout places its children in a grid. GridLayout adds properties to each child: col, row, colspan, rowspan. You can control the position of children with col and row. If col or row aren’t specified, they are automatically computed such that the item is next to the previous item, in the same row. Alternatively, the item can be put in a Row element.

Properties#

  • spacing (in length): The distance between the elements in the layout.

  • padding (in length): The padding within the layout.

  • padding-left, padding-right, padding-top and padding-bottom (in length): Set these properties to override the padding on specific sides.

Examples#

This example uses the Row element:

export component Foo inherits Window {
    width: 200px;
    height: 200px;
    GridLayout {
        spacing: 5px;
        Row {
            Rectangle { background: red; }
            Rectangle { background: blue; }
        }
        Row {
            Rectangle { background: yellow; }
            Rectangle { background: green; }
        }
    }
}

This example uses the col and row properties

export component Foo inherits Window {
    width: 200px;
    height: 150px;
    GridLayout {
        Rectangle { background: red; }
        Rectangle { background: blue; }
        Rectangle { background: yellow; row: 1; }
        Rectangle { background: green; }
        Rectangle { background: black; col: 2; row: 0; }
    }
}

Image#

An Image can be used to represent an image loaded from a file.

Properties#

  • colorize (in brush): When set, the image is used as an alpha mask and is drawn in the given color (or with the gradient).

  • image-fit (in enum ImageFit): Specifies how the source image shall be fit into the image element. (default value: contain when the Image element is part of a layout, fill otherwise)

  • image-rendering (in enum ImageRendering): Specifies how the source image will be scaled. (default value: smooth)

  • rotation-angle (in angle), rotation-origin-x (in length), rotation-origin-y (in length): Rotates the image by the given angle around the specified origin point. The default origin point is the center of the element. When these properties are set, the Image can’t have children.

  • source (in image): The image to load. Use the @image-url("...") macro to specify the location of the image.

  • source-clip-x, source-clip-y, source-clip-width, source-clip-height (in int): Properties in source image coordinates that define the region of the source image that is rendered. By default the entire source image is visible:

    Property

    Default Binding

    source-clip-x

    0

    source-clip-y

    0

    source-clip-width

    source.width - source-clip-x

    source-clip-height

    source.height - source-clip-y

  • width, height (in length): The width and height of the image as it appears on the screen.The default values are the sizes provided by the source image. If the Image is not in a layout and only one of the two sizes are specified, then the other defaults to the specified value scaled according to the aspect ratio of the source image.

Example#

export component Example inherits Window {
    width: 100px;
    height: 100px;
    VerticalLayout {
        Image {
            source: @image-url("https://slint.dev/logo/slint-logo-full-light.svg");
            // image-fit default is `contain` when in layout, preserving aspect ratio
        }
        Image {
            source: @image-url("https://slint.dev/logo/slint-logo-full-light.svg");
            colorize: red;
        }
    }
}

Scaled while preserving the aspect ratio:

export component Example inherits Window {
    width: 100px;
    height: 150px;
    VerticalLayout {
        Image {
            source: @image-url("https://slint.dev/logo/slint-logo-full-light.svg");
            width: 100px;
            // implicit default, preserving aspect ratio:
            // height: self.width * natural_height / natural_width;
        }
    }
}

Path#

The Path element allows rendering a generic shape, composed of different geometric commands. A path shape can be filled and outlined.

When not part of a layout, its width or height defaults to 100% of the parent element when not specified.

A path can be defined in two different ways:

  • Using SVG path commands as a string

  • Using path command elements in .slint markup.

The coordinates used in the geometric commands are within the imaginary coordinate system of the path. When rendering on the screen, the shape is drawn relative to the x and y properties. If the width and height properties are non-zero, then the entire shape is fit into these bounds - by scaling accordingly.

Common Path Properties#

  • fill (in brush): The color for filling the shape of the path.

  • fill-rule (in enum FillRule): The fill rule to use for the path. (default value: nonzero)

  • stroke (in brush): The color for drawing the outline of the path.

  • stroke-width (in length): The width of the outline.

  • width (in length): If non-zero, the path will be scaled to fit into the specified width.

  • height (in length): If non-zero, the path will be scaled to fit into the specified height.

  • viewbox-x/viewbox-y/viewbox-width/viewbox-height (in float) These four properties allow defining the position and size of the viewport of the path in path coordinates.

    If the viewbox-width or viewbox-height is less or equal than zero, the viewbox properties are ignored and instead the bounding rectangle of all path elements is used to define the view port.

  • clip (in bool): By default, when a path has a view box defined and the elements render outside of it, they are still rendered. When this property is set to true, then rendering will be clipped at the boundaries of the view box. This property must be a literal true or false (default value: false)

Path Using SVG commands#

SVG is a popular file format for defining scalable graphics, which are often composed of paths. In SVG paths are composed using commands, which in turn are written in a string. In .slint the path commands are provided to the commands property. The following example renders a shape consists of an arc and a rectangle, composed of line-to, move-to and arc commands:

export component Example inherits Path {
    width: 100px;
    height: 100px;
    commands: "M 0 0 L 0 100 A 1 1 0 0 0 100 100 L 100 0 Z";
    stroke: red;
    stroke-width: 1px;
}

The commands are provided in a property:

  • commands (in string): A string providing the commands according to the SVG path specification.

Path Using SVG Path Elements#

The shape of the path can also be described using elements that resemble the SVG path commands but use the .slint markup syntax. The earlier example using SVG commands can also be written like that:

export component Example inherits Path {
    width: 100px;
    height: 100px;
    stroke: blue;
    stroke-width: 1px;

    MoveTo {
        x: 0;
        y: 0;
    }
    LineTo {
        x: 0;
        y: 100;
    }
    ArcTo {
        radius-x: 1;
        radius-y: 1;
        x: 100;
        y: 100;
    }
    LineTo {
        x: 100;
        y: 0;
    }
    Close {
    }
}

Note how the coordinates of the path elements don’t use units - they operate within the imaginary coordinate system of the scalable path.

MoveTo Sub-element for Path#

The MoveTo sub-element closes the current sub-path, if present, and moves the current point to the location specified by the x and y properties. Subsequent elements such as LineTo will use this new position as their starting point, therefore this starts a new sub-path.

Properties#
  • x (in float): The x position of the new current point.

  • y (in float): The y position of the new current point.

LineTo Sub-element for Path#

The LineTo sub-element describes a line from the path’s current position to the location specified by the x and y properties.

Properties#
  • x (in float): The target x position of the line.

  • y (in float): The target y position of the line.

ArcTo Sub-element for Path#

The ArcTo sub-element describes the portion of an ellipse. The arc is drawn from the path’s current position to the location specified by the x and y properties. The remaining properties are modelled after the SVG specification and allow tuning visual features such as the direction or angle.

Properties#
  • large-arc (in bool): Out of the two arcs of a closed ellipse, this flag selects that the larger arc is to be rendered. If the property is false, the shorter arc is rendered instead.

  • radius-x (in float): The x-radius of the ellipse.

  • radius-y (in float): The y-radius of the ellipse.

  • sweep (in bool): If the property is true, the arc will be drawn as a clockwise turning arc; anti-clockwise otherwise.

  • x-rotation (in float): The x-axis of the ellipse will be rotated by the value of this properties, specified in as angle in degrees from 0 to 360.

  • x (in float): The target x position of the line.

  • y (in float): The target y position of the line.

CubicTo Sub-element for Path#

The CubicTo sub-element describes a smooth Bézier from the path’s current position to the location specified by the x and y properties, using two control points specified by their respective properties.

Properties#
  • control-1-x (in float): The x coordinate of the curve’s first control point.

  • control-1-y (in float): The y coordinate of the curve’s first control point.

  • control-2-x (in float): The x coordinate of the curve’s second control point.

  • control-2-y (in float): The y coordinate of the curve’s second control point.

  • x (in float): The target x position of the curve.

  • y (in float): The target y position of the curve.

QuadraticTo Sub-element for Path#

The QuadraticTo sub-element describes a smooth Bézier from the path’s current position to the location specified by the x and y properties, using the control points specified by the control-x and control-y properties.

Properties#
  • control-x (in float): The x coordinate of the curve’s control point.

  • control-y (in float): The y coordinate of the curve’s control point.

  • x (in float): The target x position of the curve.

  • y (in float): The target y position of the curve.

Close Sub-element for Path#

The Close element closes the current sub-path and draws a straight line from the current position to the beginning of the path.

Rectangle#

By default, a Rectangle is just an empty item that shows nothing. By setting a color or configuring a border, it’s then possible to draw a rectangle on the screen.

When not part of a layout, its width and height default to 100% of the parent element.

Properties#

  • background (in brush): The background brush of this Rectangle, typically a color. (default value: transparent)

  • border-color (in brush): The color of the border. (default value: transparent)

  • border-radius (in length): The size of the radius. (default value: 0)

  • border-width (in length): The width of the border. (default value: 0)

  • clip (in bool): By default, when an element is bigger or outside another element, it’s still shown. When this property is set to true, the children of this Rectangle are clipped to the border of the rectangle. (default value: false)

Example#

export component Example inherits Window {
    width: 270px;
    height: 100px;

    Rectangle {
        x: 10px;
        y: 10px;
        width: 50px;
        height: 50px;
        background: blue;
    }

    // Rectangle with a border
    Rectangle {
        x: 70px;
        y: 10px;
        width: 50px;
        height: 50px;
        background: green;
        border-width: 2px;
        border-color: red;
    }

    // Transparent Rectangle with a border and a radius
    Rectangle {
        x: 140px;
        y: 10px;
        width: 50px;
        height: 50px;
        border-width: 4px;
        border-color: black;
        border-radius: 10px;
    }

    // A radius of width/2 makes it a circle
    Rectangle {
        x: 210px;
        y: 10px;
        width: 50px;
        height: 50px;
        background: yellow;
        border-width: 2px;
        border-color: blue;
        border-radius: self.width/2;
    }
}

TextInput#

The TextInput is a lower-level item that shows text and allows entering text.

When not part of a layout, its width or height defaults to 100% of the parent element when not specified.

Properties#

  • color (in brush): The color of the text (default value: depends on the style)

  • font-family (in string): The name of the font family selected for rendering the text.

  • font-size (in length): The font size of the text.

  • font-weight (in int): The weight of the font. The values range from 100 (lightest) to 900 (thickest). 400 is the normal weight.

  • font-italic (in bool): Whether or not the font face should be drawn italicized or not. (default value: false)

  • has-focus (out bool): TextInput sets this to true when it’s focused. Only then it receives KeyEvents.

  • horizontal-alignment (in enum TextHorizontalAlignment): The horizontal alignment of the text.

  • input-type (in enum InputType): Use this to configure TextInput for editing special input, such as password fields. (default value: text)

  • letter-spacing (in length): The letter spacing allows changing the spacing between the glyphs. A positive value increases the spacing and a negative value decreases the distance. (default value: 0)

  • read-only (in bool): When set to true, text editing via keyboard and mouse is disabled but selecting text is still enabled as well as editing text programatically. (default value: false)

  • selection-background-color (in color): The background color of the selection.

  • selection-foreground-color (in color): The foreground color of the selection.

  • single-line (in bool): When set to true, the text is always rendered as a single line, regardless of new line separators in the text. (default value: true)

  • text-cursor-width (in length): The width of the text cursor. (default value: provided at run-time by the selected widget style)

  • text (in-out string): The text rendered and editable by the user.

  • vertical-alignment (in enum TextVerticalAlignment): The vertical alignment of the text.

  • wrap (in enum TextWrap): The way the text input wraps. Only makes sense when single-line is false. (default value: no-wrap)

Functions#

  • focus() Call this function to focus the text input and make it receive future keyboard events.

  • select-all() Selects all text.

  • clear-selection() Clears the selection.

  • copy() Copies the selected text to the clipboard.

  • cut() Copies the selected text to the clipboard and removes it from the editable area.

  • paste() Pastes the text content of the clipboard at the cursor position.

Callbacks#

  • accepted(): Invoked when enter key is pressed.

  • cursor-position-changed(Point): The cursor was moved to the new (x, y) position.

  • edited(): Invoked when the text has changed because the user modified it.

Example#

export component Example inherits Window {
    width: 270px;
    height: 100px;

    TextInput {
        text: "Replace me with a name";
    }
}

Text#

The Text element is responsible for rendering text. Besides the text property, that specifies which text to render, it also allows configuring different visual aspects through the font-family, font-size, font-weight and color properties.

The Text element can break long text into multiple lines of text. A line feed character (\n) in the string of the text property will trigger a manual line break. For automatic line breaking you need to set the wrap property to a value other than no-wrap, and it’s important to specify a width and height for the Text element, in order to know where to break. It’s recommended to place the Text element in a layout and let it set the width and height based on the available screen space and the text itself.

Properties#

  • color (in brush): The color of the text. (default value: depends on the style)

  • font-family (in string): The name of the font family selected for rendering the text.

  • font-size (in length): The font size of the text.

  • font-weight (in int): The weight of the font. The values range from 100 (lightest) to 900 (thickest). 400 is the normal weight.

  • font-italic (in bool): Whether or not the font face should be drawn italicized or not. (default value: false)

  • horizontal-alignment (in enum TextHorizontalAlignment): The horizontal alignment of the text.

  • letter-spacing (in length): The letter spacing allows changing the spacing between the glyphs. A positive value increases the spacing and a negative value decreases the distance. (default value: 0)

  • overflow (in enum TextOverflow): What happens when the text overflows (default value: clip).

  • text (in string): The text rendered.

  • vertical-alignment (in enum TextVerticalAlignment): The vertical alignment of the text.

  • wrap (in enum TextWrap): The way the text wraps (default value: no-wrap).

Example#

This example shows the text “Hello World” in red, using the default font:

export component Example inherits Window {
    width: 270px;
    height: 100px;

    Text {
        x:0;y:0;
        text: "Hello World";
        color: red;
    }
}

This example breaks a longer paragraph of text into multiple lines, by setting a wrap policy and assigning a limited width and enough height for the text to flow down:

export component Example inherits Window {
    width: 270px;
    height: 300px;

    Text {
        x:0;
        text: "This paragraph breaks into multiple lines of text";
        wrap: word-wrap;
        width: 150px;
        height: 100%;
    }
}

TouchArea#

Use TouchArea to control what happens when the region it covers is touched or interacted with using the mouse.

When not part of a layout, its width or height default to 100% of the parent element.

Properties#

  • has-hover (out bool): TouchArea sets this to true when the mouse is over it.

  • mouse-cursor (in enum MouseCursor): The mouse cursor type when the mouse is hovering the TouchArea.

  • mouse-x, mouse-y (out length): Set by the TouchArea to the position of the mouse within it.

  • pressed-x, pressed-y (out length): Set by the TouchArea to the position of the mouse at the moment it was last pressed.

  • pressed (out bool): Set to true by the TouchArea when the mouse is pressed over it.

Callbacks#

  • clicked(): Invoked when clicked: The mouse is pressed, then released on this element.

  • moved(): The mouse has been moved. This will only be called if the mouse is also pressed.

  • pointer-event(PointerEvent): Invoked when a button was pressed or released.

Example#

export component Example inherits Window {
    width: 200px;
    height: 100px;
    area := TouchArea {
        width: parent.width;
        height: parent.height;
        clicked => {
            rect2.background = #ff0;
        }
    }
    Rectangle {
        x:0;
        width: parent.width / 2;
        height: parent.height;
        background: area.pressed ? blue: red;
    }
    rect2 := Rectangle {
        x: parent.width / 2;
        width: parent.width / 2;
        height: parent.height;
    }
}

VerticalLayout and HorizontalLayout#

These layouts place their children next to each other vertically or horizontally. The size of elements can either be fixed with the width or height property, or if they aren’t set they will be computed by the layout respecting the minimum and maximum sizes and the stretch factor.

Properties#

  • spacing (in length): The distance between the elements in the layout.

  • padding (in length): the padding within the layout.

  • padding-left, padding-right, padding-top and padding-bottom (in length): Set these properties to override the padding on specific sides.

  • alignment (in enum LayoutAlignment): Set the alignment. Matches the CSS flex box.

Example#

export component Foo inherits Window {
    width: 200px;
    height: 100px;
    HorizontalLayout {
        spacing: 5px;
        Rectangle { background: red; width: 10px; }
        Rectangle { background: blue; min-width: 10px; }
        Rectangle { background: yellow; horizontal-stretch: 1; }
        Rectangle { background: green; horizontal-stretch: 2; }
    }
}

Window#

Window is the root of the tree of elements that are visible on the screen.

The Window geometry will be restricted by its layout constraints: Setting the width will result in a fixed width, and the window manager will respect the min-width and max-width so the window can’t be resized bigger or smaller. The initial width can be controlled with the preferred-width property. The same applies to the Windows height.

Properties#

  • always-on-top (in bool): Whether the window should be placed above all other windows on window managers supporting it.

  • background (in brush): The background brush of the Window. (default value: depends on the style)

  • default-font-family (in string): The font family to use as default in text elements inside this window, that don’t have their font-family property set.

  • default-font-size (in-out length): The font size to use as default in text elements inside this window, that don’t have their font-size property set. The value of this property also forms the basis for relative font sizes.

  • default-font-weight (in int): The font weight to use as default in text elements inside this window, that don’t have their font-weight property set. The values range from 100 (lightest) to 900 (thickest). 400 is the normal weight.

  • icon (in image): The window icon shown in the title bar or the task bar on window managers supporting it.

  • no-frame (in bool): Whether the window should be borderless/frameless or not.

  • title (in string): The window title that is shown in the title bar.