Currently, hatch only from closed loops of edges:
1, each edge must be a complete line, arc, circle, elliptical arc, or an eclipse;
2, for circle, ellipse cases, each complete curve defines a loop;
3, for non-cosed curves, each loop must be formed by joining start/end point of edges;
4, no loop crossing: a loop cannot cross itself or another loop;
5, a loop may touch another loop;
6, sharing start/end points between two loops is allowed.
We may want to support enclosed areas of selected curves, but there's no developer working on it, as far as i am aware of.
demis wrote
Is there any analogue to AutoCAD's "boundary" command, which does in fact allow one to "fill" an area enclosed by crossing lines/shapes (you click in the enclosed area, just like a Paint Bucket tool)? I know 'hatch' is not exactly that, since it fills an object, not any shape visible in the view.
I have personally found that the Boundary command is the most useful command, since it is much simpler than boolean operations, and simple to use.