Adobe Live Cycle Designer - How to update the custom defined property(meta data) on onclick event of the formfield button.

[URaja]

Added custom property(metadata) to the form.   formfinalized=fasle.

Now on onclick event of the formfield

I do see the property along with other metadata

var Meta = event.target.metadata;
xfa.host.messageBox(Meta, "Metadata of this form", 3,0);

Now want to update formfinalized=true when button is clicked "Form1.Header.Buttons.Sign::click - (JavaScript, client)