dynamic xtag

Experimental support for web components. This field stores a reference to the component implementation. It was inspired by Mozilla's x-tags project. Please note: in the future it may be possible to extend Element from your class, in which case this field will be deprecated.

If xtag has not been set, it will simply return this Element.

Source 

// Note: return type is `dynamic` for convenience to suppress warnings when
// members of the component are used. The actual type is a subtype of Element.
get xtag => _xtag != null ? _xtag : this;
void xtag=(Element value)

Source 

set xtag(Element value) {
  _xtag = value;
}