metadatio v6.0.0

        super.addField(new Field({
            name: 'name',
            dataType: DataTypes.string,
            validators: {
                'pattern': new Validator(ValidatorTypes.regex, /^_?(\d|[a-zA-Z]|_|-)$/i),
                'lengths': new Validator(ValidatorTypes.lengths, { min: 2, max: 64 }
            }
        }));
    }

    static getInstance() {
        Foo.instance = new Foo();
        return Foo.instance;
    }
}

        ...
    }

    ...
}

        super.addField(new Field({
            name: 'foo',
            dataType: Foo.getInstance(),
            multiplicity: 'many'
        }));
    }

    ...
}

module.exports = {
    Foo: Foo.getInstance(),
    Bar: Bar.getInstance()
};

# and include it on your consumer projects
npm install --save my-project-metadata

let testItem = {
    name: 'test-value';
}
Foo.validate(testItem); // Returns true

testItem.name = '123n';
Foo.validate(testItem); // Returns false

There are several ongoing projects for building up some extensions of Metadatio core: