Cannot parse with webidl2 because B implements A doesn't seem to be valid syntax

[Ohems]

Trying to parse the ammo.idl file last updated in commit 1a601e4 with the WebIDL2.js online checker yields the following error:

WebIDLParseError: Syntax error at line 49, since `interface btVector4`:
btVector4 implements btVector3;
^ Unrecognised tokens

Inheritance is currently done with

interface A {};
interface B {};
B implements A;

while according to the WebIDL specification it should apparently be done with

interface A {};
interface B : A {};

I wonder if this is a bug in the WebIDL2.js library or in this one as I'm not experienced in WebIDL.