Copyright of the IDL Definitions

Here is a question about the copyright issues involved when creating a DOM
implementation.

The copyright notice
http://www.w3.org/TR/REC-DOM-Level-1/copyright-notice.html forbids the
creation of "modifications or derivatives". My perception is that the
creation of a DOM implementation involves making a derivative work of the
DOM API published in
http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html or
http://www.w3.org/TR/REC-DOM-Level-1/idl-definitions.html . These files
are published under the mentioned copyright notice, so how can any legal
DOM (level 1) implementation exist? 

Regarding DOM level 2, there is a distinction between the "document" and
the "bindings", with the latter being published under a different license
that permits modifications. The copyright notice
http://www.w3.org/TR/DOM-Level-2/copyright-notice.html explicitly mentions
the "IDL binding", while the table of contents speeks of "Java Language
Binding" and "ECMA Script Language Binding", but "IDL Definitions" instead
of IDL binding. Are these "IDL Definitions" really meant by the term "IDL
binding", and if they are, could this be made more clear in the level 2
document?

Thanks for your thoughts,

Tobias