Bugzilla – Bug 15346
"(Node or DOMString)..." is not valid WebIDL
Last modified: 2011-12-27 15:04:02 UTC
void prepend((Node or DOMString)... nodes);
As with the enum, this a) leaves precise error-handling behavior undefined, and b) makes it impossible to process the IDLs automatically (such as with idlharness.js). Please either get WebIDL changed to allow this syntax, or use "any" for now and define the precise behavior in prose.
My bad, looks like a recent WebIDL change.