A variable width is written only as the same reach on both sides of the path (a
point with unequal sides drew nothing elsewhere). A stroke wider on one side, on a
shape that shows nothing else, is written as a vector filled with the area it
paints, with the stroke itself kept as plugin data that the import puts back.
Bound layer and text fields also name the number of the field they set. Docs: text,
effect and grid styles and symmetric variable widths are checked; non-colour
bindings come across as values.