Line labels
A line label is a shape object that has been attached to a line.
When you click a connection line with the Text tool, a line label is created. But this is not the only way to create one. Any shape object can become a line label; drag a shape to a line and drop it there when the line becomes highlighted. This works only if the line is set in the Connections inspector to allow labels. A line label can be removed by dragging it away from the line.
A line label stays attached to its line until you remove it; this means you can move or reroute the line without losing the labels.
You can change the position and orientation of a line label with the Geometry inspector. You can also press the arrow keys to adjust the location and offset of the selected line label; note that the Right arrow always means "toward the head of the line", regardless of whether the line is pointing to the right or not.