Function
The string to test
true for an absolute http(s) URL, false for anything else
Exported because callers outside the domain need to ask the SAME question the boundary asks. A content key is resolved through the store, but a value that is already an absolute URL — a lesson served by YouTube — must be left alone; resolving it would prepend the store's base and produce nonsense. A second, private definition of "absolute URL" could drift from this one and let a value pass the bypass yet fail urlOrRelativePath.
Narrower than urlOrRelativePath: a site-relative path such as
/local-filesystem-lesson/x.mp4 is a valid value there and is false here.
Whether a string is a fully-qualified
http:orhttps:URL.