Making it work within the same browser window is supported out of the box, cf. bpmn-js#97e1ad14
.
The trick is to share a clipboard
module across multiple bpmn-js instances like so:
var clipboardModule = {
'clipboard': [ 'value', new Clipboard() ]
};
m2 = new Modeler({
additionalModules: [
clipboardModule
]
});
m1 = new Modeler({
additionalModules: [
clipboardModule
]
});