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