Example: web.concurrent_start
In the following example, the concurrent_start function marks the beginning of a concurrent group.
web.concurrent_start(null); web.add_header(...); web.url(..., "URL=http://...url1", new String[]{ ...); web.add_header(...); web.add_header(...); web.url(..., "URL=http://...url2", new String[]{ ...); web.concurrent_end(null);