The parser callback system is too coarse-grained

[jcbollinger]

The parser's syntax-level callbacks are too coarse-grained to accurately reflect the details of whitespace inside complex data values. This makes it impossible for cif_linguist, say, to accurately preserve whitespace in CIF 2 or STAR 2 input.

[jcbollinger]

Recasting the nature of the whitespace callback and the meaning of zero-length whitespace runs permits cif_linguist to accurately preserve whitespace. It's still a bit tricky and cumbersome, but it works well enough.

I am leaving this issue open for the time being, however, to suggest coming back to it when the next major revision is planned.