See the Semantics page. I guess we'll have to define the HLL as multiple extensions to existing languages, then refine it to obtain cleaner things. All this is pure draft. But the compiler ought to eventually support them. Non-Concerns Syntax matters in as much as we need it to communicate the semantics below.
Textual syntax is sequential just because text is sequential.
However, it looks like some bottleneck forces individual humans to acquire data in a sequential manner, anyway. Being able to automatically juggle between multiple syntax has always been a goal of Tunes. It also looks quite natural to me that the preferred syntax for input be not forcibly the preferred syntax for output. For instance, I'd like free-form keyboard input with name completion, and nicknames, but structured output with full names and color. For the sake of consistency verification, it should be easy to interactively change the syntactic mode.