margin figure's label counter

[Ehud Behar]

I want to define a new float in my document - margin figure.

I defined a new float using a module file with a Style:

Float
Type marginfigure
GuiName MarginFigure
NumberWithin figure # <————
RefPrefix fig
more commands etc.
End

The document class is book, and inside chapter 1, as you can see in the attached image, I inserted a regular figure, followed by a margin figure. The margin figure counter in the editor is 1.1.1, since it is in chapter one, and it inherited the first number inside the figure counter.

I want the margin figure to have the label 1.2 (which logically makes more sense if you treat figure and marginfigure on an equal footing).

What amendments should I make to the Style to get it changed the way I want?
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