Assertion:
There is an attribute that Microsoft's references list for this element called BORDER. It does appear to have some effect, but it appears to be to render padding around the frame (which is what the HSPACE and VSPACE attributes accomplish) instead of rendering a distinct border around the frame.

Simple IFRAME, no BORDER attribute applied:
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Simple IFRAME, BORDER=0 attribute applied:
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Simple IFRAME, BORDER=1 attribute applied:
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Simple IFRAME, BORDER=10 attribute applied:
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Simple IFRAME, BORDER=30 attribute applied:
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