In the following example the TextField inside Field2 should be stretched to fit the width, but it doesn't happen:
Code:Html.X().Panel()
.Layout(LayoutType.Form)
.Items(
Html.X().TextField()
.FieldLabel("Field1")
,
Html.X().FieldContainer()
.FieldLabel("Field2")
.Layout(LayoutType.HBox)
.Items(
Html.X().TextField().Flex(1)
)
)