- Before version 13.0, this module had a feature allowing to change the
  color of a line depending on a field, using a `colors` attribute with
  the name of the field on the `<tree>` element. Since 13.0, the
  `colors` attribute is no longer in the RelaxNG schema of the tree
  view, so we can't use it anymore. This feature has then been dropped,
  but could be reimplement in another way.
- Since version 17.0 coloring is written into ``style`` attribute of (td) element
