cop.create('AddressLayer')
.refineClass(Person, {
    address: function() {
        return 'Prof.-Dr.-Helmert Str.'
    },
    toString: function() {
        var secret = 'foo'
        return cop.proceed() +
        ' (' + this.address() + ')';
    },
});

cop.create('EmployerLayer')
.refineClass(Person, {
    employer: function() { return 'HPI' },
    toString: function() {
        alert(secret)
        return cop.proceed() +
        ' (' + this.employer() + ')';
    },
});

Object.subclass('Person', {
    toString: function() {
        return 'Person(' +
            this.name + ')'
    },
})

reset

AddressLayer.flattened()

EmployerLayer.flattened()

COP great for development but
  - Considerable performance impact
  - When used only for development, layer has to be merged manually

Merge definitions of layer into base layer automatically
  - Add new properties and methods
  - Replace properties and methods that do not proceed
  - Merge methods of base layer into new methods when proceed is used