This class is used to set the position and size of child elements.

Each child element has three values associated with each axis: {left, right, width} on the horizontal axis, and {top, bottom, height} on the vertical axis. Precisely two of three values may be set at a time, or the system will be over- or under-contrained. For this reason, the following methods are provided for setting these values:

• {@link Layout.Layer#setLeftRight}
• {@link Layout.Layer#setLeftWidth}
• {@link Layout.Layer#setRightWidth}
• {@link Layout.Layer#setTopBottom}
• {@link Layout.Layer#setTopHeight}
• {@link Layout.Layer#setBottomHeight}

By default, each layer is set to fill the entire parent (i.e., {left, top, right, bottom} = {0, 0, 0, 0}).

class Layer {
 dart_html.Element container, child;
 Object userObject;

 bool setLeft = false, setRight = false, setTop = false, setBottom = false, setWidth = false, setHeight = false;
 bool setTargetLeft = true, setTargetRight = true, setTargetTop = true,
     setTargetBottom = true, setTargetWidth = false, setTargetHeight = false;
 Unit leftUnit, topUnit, rightUnit, bottomUnit, widthUnit, heightUnit;
 Unit targetLeftUnit = Unit.PX, targetTopUnit = Unit.PX, targetRightUnit = Unit.PX,
     targetBottomUnit = Unit.PX, targetWidthUnit, targetHeightUnit;
 double left = 0.0, top = 0.0, right = 0.0, bottom = 0.0, width = 0.0, height = 0.0;
 double sourceLeft = 0.0, sourceTop = 0.0, sourceRight = 0.0, sourceBottom = 0.0, sourceWidth = 0.0,
 sourceHeight = 0.0;
 double targetLeft = 0.0, targetTop = 0.0, targetRight = 0.0, targetBottom = 0.0, targetWidth = 0.0,
 targetHeight = 0.0;

 Alignment hPos = Alignment.STRETCH, vPos = Alignment.STRETCH;
 bool visible = true;

 Layer(dart_html.Element container, dart_html.Element child, Object userObject) {
   this.container = container;
   this.child = child;
   this.userObject = userObject;
 }

 /**
  * Gets the container element associated with this layer.
  *
  * <p>
  * This is the element that sits between the parent and child elements. It
  * is normally necessary to operate on this element only when you need to
  * modify CSS properties that are not directly modeled by the Layer class.
  * </p>
  *
  * @return the container element
  */
 dart_html.Element getContainerElement() {
   return container;
 }

 /**
  * Gets the user-data associated with this layer.
  *
  * @return the layer's user-data object
  */
 Object getUserObject() {
   return this.userObject;
 }

 /**
  * Sets the layer's bottom and height values.
  *
  * @param bottom
  * @param bottomUnit
  * @param height
  * @param heightUnit
  */
 void setBottomHeight(double bottom, Unit bottomUnit, double height,
                      Unit heightUnit) {
   this.setTargetBottom = this.setTargetHeight = true;
   this.setTargetTop = false;
   this.targetBottom = bottom;
   this.targetHeight = height;
   this.targetBottomUnit = bottomUnit;
   this.targetHeightUnit = heightUnit;
 }

 /**
  * Sets the child element's horizontal position within the layer.
  *
  * @param position
  */
 void setChildHorizontalPosition(Alignment position) {
   this.hPos = position;
 }

 /**
  * Sets the child element's vertical position within the layer.
  *
  * @param position
  */
 void setChildVerticalPosition(Alignment position) {
   this.vPos = position;
 }

 /**
  * Sets the layer's left and right values.
  *
  * @param left
  * @param leftUnit
  * @param right
  * @param rightUnit
  */
 void setLeftRight(double left, Unit leftUnit, double right,
                   Unit rightUnit) {
   this.setTargetLeft = this.setTargetRight = true;
   this.setTargetWidth = false;
   this.targetLeft = left;
   this.targetRight = right;
   this.targetLeftUnit = leftUnit;
   this.targetRightUnit = rightUnit;
 }

 /**
  * Sets the layer's left and width values.
  *
  * @param left
  * @param leftUnit
  * @param width
  * @param widthUnit
  */
 void setLeftWidth(double left, Unit leftUnit, double width,
                   Unit widthUnit) {
   this.setTargetLeft = this.setTargetWidth = true;
   this.setTargetRight = false;
   this.targetLeft = left;
   this.targetWidth = width;
   this.targetLeftUnit = leftUnit;
   this.targetWidthUnit = widthUnit;
 }

 /**
  * Sets the layer's right and width values.
  *
  * @param right
  * @param rightUnit
  * @param width
  * @param widthUnit
  */
 void setRightWidth(double right, Unit rightUnit, double width,
                    Unit widthUnit) {
   this.setTargetRight = this.setTargetWidth = true;
   this.setTargetLeft = false;
   this.targetRight = right;
   this.targetWidth = width;
   this.targetRightUnit = rightUnit;
   this.targetWidthUnit = widthUnit;
 }

 /**
  * Sets the layer's top and bottom values.
  *
  * @param top
  * @param topUnit
  * @param bottom
  * @param bottomUnit
  */
 void setTopBottom(double top, Unit topUnit, double bottom,
                   Unit bottomUnit) {
   this.setTargetTop = this.setTargetBottom = true;
   this.setTargetHeight = false;
   this.targetTop = top;
   this.targetBottom = bottom;
   this.targetTopUnit = topUnit;
   this.targetBottomUnit = bottomUnit;
 }

 /**
  * Sets the layer's top and height values.
  *
  * @param top
  * @param topUnit
  * @param height
  * @param heightUnit
  */
 void setTopHeight(double top, Unit topUnit, double height,
                   Unit heightUnit) {
   this.setTargetTop = this.setTargetHeight = true;
   this.setTargetBottom = false;
   this.targetTop = top;
   this.targetHeight = height;
   this.targetTopUnit = topUnit;
   this.targetHeightUnit = heightUnit;
 }

 /**
  * Sets the layer's visibility.
  *
  * @param visible
  */
 void setVisible(bool visible) {
   this.visible = visible;
 }
}