marginwidth attribute | marginWidth property
Sets or retrieves the left and right margin widths before displaying the text in a frame.
the width, in pixels.
Margins cannot be less than 1 pixel or so large that the text cannot be displayed.
If marginWidth is specified but marginHeight is not, marginHeight is set to 0.
If the document hosted in the frame or iframe has margin-left or margin-right properties set either through Cascading Style Sheets (CSS) or through the leftMargin or rightMargin properties of the body element, then this property is ignored.