Things to consider:
- indexing of sequences
- BaseType[:] raises exception, we need BaseType.data

- Check GRADS plugin

Responses:
- netCDF
- Excel
- Google Spreadsheets

WMS response:
- transparent gifs
- generate plots for inner variables of sequences, using color for value

SQL plugin:
- dapper-compliant; check Gui's data.

DAS response:
- remove numpy code (tolist(), eg). Force plugins to set attributes as list or tuple.

helper:
- edit ``constrain`` to call .filter() method in sequences.
