[whatwg] Using the HTML5 DOCTYPE as a new quirksmode switch

[Martin Atkins]

Asbjørn Ulsberg wrote:
>  Improving on the legacy, proprietary DOM just isn't feasible, imo.
> 

Are there particular parts that overlap between IE's DOM and the 
standard DOM where IE's implementation is non-compliant?

If not, why can't IE simply support both sets of methods at the same 
time? (In other words, add the standard DOM classes, methods and events 
while leaving in all of the proprietary stuff that people depend on.)