Per the standards, scheduling and prioritization of downloads is up to browsers.
The standard also defines that scripts that are not async have to be executed before later content can be parsed (because they can document.write()). They can still be loaded with any priority the browser wants; they just need to block observable DOM construction.
The standard also defines that scripts that are not async have to be executed before later content can be parsed (because they can document.write()). They can still be loaded with any priority the browser wants; they just need to block observable DOM construction.