- everything that is part of the drawing should be plain SVG (strictly following the SVG specification) to assure that every SVG program can handle it (e.g. Internet browsers).
The hatch patterns however contained old stuff like traces of Sodipodi that might be a problem in the future.
- negative scale and line width is not sensible and lead to strange effects thus set a minimum
- set the minimum reasonably above 0 since e.g. a hatch scale of 0.01 fills 8 GB RAM -> out of RAM error
- disable KeyboardTracking since we don't want a time-consuming recomputation while the user changes a value