Roadmap
-------
Version 0.003
- error processing
- parameter validation

Version 0.004
- text basics

Version 0.005
- gradients and patterns
- clipping paths
- masks

The following list contains some things I don't want to
forget. There are many possibly much more important things to do
which are not listed here because I won't forget them.

- Params::Validate consequently
- consequently use in_error where required
- stricter on percentage in colors
- explicit return in all methods
- document engine_class attribute
- introduce engine_args attribute
- documentation on SVG validation.
- ID and NMTOKEN in %ATTR_VAL

done
----
- get rid of width/height setting via SVG::Render
- weaken some references (currently not necessary)
- document that 0 width and height are ignored (at least in topmost
  settings)
- remove white space from attribute values (or not?)
- Acknowledge Cairo library, Perl Cairo module, SVG
- Correct hook docu.
- refer to CHANGES from README
- document which DOM functions have to be provided by an input
  object
- homogenize parameters for SVG::Rasterize and the rasterize method
- homogenize interface docu of methods
- consequent assignments in interface docu of methods with return
  value
- regex for engine_class
- svg validation via interface, not class
- revise _create_engine, class name validation, width/height
- callbacks etc. in %ATTR_VAL
- color regexes in Regexes
- probably, the transformation matrix has to be applied by cairo
  (-> text, stroke-width in general).
- check rotation direction in spec
- property validation with dedicated %PROP_VAL? - not for now
  -> specific for xsl / css
  -> apply to whole hash after setting of defaults?
  -> element specific?
- rest of path commands
- support for stroke properties (linecap etc.)
- stroke-dasharray and stroke-dashoffset
- clamp color values only at presentation time
- update docu: The state is not that much proof of concept any more.
- method _in_error needs to be public (to be used by State).
- document all regexes
- validation possible for those attributes that still have type
  CDATA? - Some stuff will have to (further) validated in State or
  Rasterize. However, the engine should get clean stuff.