@All - For completeness: https://helpandsupport.xara.com/xara...=line%20widths
Note: A zero width line is a special case, and should not normally be used. This draws a line one device-pixel wide. The actual size will therefore depend on the device the drawing is displayed on. On a monitor screen one pixel is clearly visible and is never shown anti-aliased. On devices such as printers and particularly on image setters, which have a much higher resolution, the line is almost invisible (zero width lines in imported files are converted to 0.25pt).
Funny how Xara fails to mention zero-width lines do not render. If the result is SVG, you have stroke-width=0. If it is a span Tag, no border attribute is included.
The last bold part is interesting too. This means you end up with a 0.333px Line width.

Acorn