IMPLEMENTED
===========

Workbook:

Sheet:
  name
  visibility
  margins (left, right, top, bottom)
  header (left, center, right)
  footer (left, center, right)

Cell:
  value (string, number, boolean)
  merged cells (column and row spans)
  formatting attributes

Row:
  height
  visibility
  formatting attributes

Column:
  width
  visibility
  formatting attributes

Format:
  horizontal alignment
  font (name, color, bold, italic, underline, strike)
  borders



TODO
====

Sheet:
  better parsing of header/footer
  margins (header, footer)
  page size, orientation

Cell:
  formula (!)
  error code
  hyperlink

Format:
  vertical alignment
  text wrapping
  rotation angle
  style


INCOMPATIBLE
============
- exact width of column
- border style: double, medium, slanted
- alignment: repeat, justified, filled, distributed
- header/footer fields, e.g &Z, font
