Expand stroke expands the stroke of a shape or line, converting the line's boundaries into paths forming a closed shape.
Drawing a line creates an open path with a skeletal structure that can be adjusted. The boundaries of a line, on the other hand cannot be edited. Expanding the stroke converts the line's boundaries into paths forming a closed shape, so you can edit them individually in the same way as a regular shape.
The expand stroke feature has a range of uses. It can be used to:
Modify the shape of strokes by adjusting its curves and nodes.
Separate a shape into its two components: its stroke and fill (without stroke outline)
Convert strokes to flattened shapes that can scale better as a flattened image, which looks more consistent across browsers.
Flatten strokes prior to SVG export in web development.
To expand a stroke:
Select the shape with either the Move Tool or the Node Tool.
Click Expand Stroke on the Layer menu.
The shape's stroke is now detached from the object and made into curves. As with Convert to Curves, the resulting curves can then be manipulated with the Node Tool.