2 questions about ES6 module loaders

[Glen]

I apologize if these are silly questions, but:

1. Do ES6 module loaders make use of the browser cache? f.e. If you 
request a JS module and that JS file is in memory/on disk, will it 
return that file instead?

2. Will ES6 module loaders set a header that indicates that the request 
is not a regular browser request? (similar to how JS libs set an 
X-Requested-With header) If not, will it be possible to add custom 
headers to such requests?

I don't really know which method browsers will use to load modules – I 
assume XMLHttpRequest is used for current polyfills, but I don't know 
what the actual implementations will use (?).

Thanks.