Thanks for the Rietveld upload.  I haven't had a chance to review this properly yet, but hope to do so within the next few days.

One question: the production list you added to the docs says:

  format_string: (`byte_order_specifier`? `type_string`)*

This suggests that format strings like '<' and '<>b' are invalid;  is that correct, or should the production list be something like:

  format_string: (`byte_order_specifier` | `type_string`)*

?  Whether these cases are valid or not (personally, I think they should be), we should add some tests for them.  '<' *is* currently valid, I believe.


The possibility of mixing native size/alignment with standard size/alignment in a single format string makes me a bit uneasy, but I can't see any actual problems that might arise from it (equally, I can't imagine why anyone would want to do it).  I wondered briefly whether padding has clear semantics when a '@' appears in the middle of a format string, but I can't see why it wouldn't have.