A polyline is a set of at least two other lines of any type (including polylines themselves). Every line must share one or two of its endpoints with the endpoints of other lines.
There are two possible ways to create a polyline, either by selecting one line and searching the rest until a corner or end is reached, or by selecting several lines (see Entity selection). In the case of the latter, the order of selection is not important but all of them must join each other by sharing common points.
Polylines are drawn in green to show the difference between the other lines, which are drawn in blue.
When deleting a polyline, all its lines are deleted. When exploding it (see Polyline), the polyline will disappear and its individual lines will appear.
It is not possible to create third level polylines: one former polyline can be included inside another, but this is the limit and these two cannot be included within a further polyline.
The Number option lets you choose the label that will be assigned to the next created line. If a line with this number already exists, its number is changed.