A manual page a day... Click here to see the manual table of contents.
You can add an arc, line, or polyline entity to an existing open polyline, forming one continuous polyline entity. To join an entity to a polyline, that entity must already share an endpoint with an end vertex of the selected polyline.
When you join an entity to a polyline, the width of the new polyline segment depends on the width of the original polyline and the type of entity you are joining to it:
A line or an arc assumes the same width as the polyline segment for the end vertex to which it is joined.
A polyline joined to a tapered polyline retains its own width values.