D1: Error: function ... cannot have an in contract when overriden function

[jicman via Digitalmars-d-learn]

On Saturday, 8 November 2014 at 01:59:56 UTC, Adam D. Ruppe wrote:
> If it is just that one error, you could always just comment out 
> the in contract and recompile.

Sorry it took so long.  Extremely busy, but anyway, this is the 
piece of the code that is causin the problem:
<code>
override void text(Dstring txt) // setter
in
{
	if(txt.length)
		assert(!this.image, "Button image with text not supported");
}
body
{
	super.text = txt;
}

alias Control.text text; // Overload.
</code>

I have no idea what these lines do. Any thoughts?  Thanks.

josé