No it's not possible. Ignoring any historical reasons, nowadays it would be considered a security vulnerability -- eg. many sites put untrusted content into iframes (the iframe source being a different origin so cannot modify the parent frame, per the same origin policy).
If such untrusted content had a mechanism to place content outside of the bounds of the iframe it could (for example) place an "identical" login div (or whatever) over a parent frame's real login fields, and could thus steal username/password information. Which would suck.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…