Break
Click a line, an arc or a circle — it splits at the point of the click.

When you need it
- To give one half its own dimension: while the segment is one, a dimension sets its whole length.
- To delete the middle of a segment without touching its ends.
What happens to the constraints
The halves meet in one shared point, so the outline stays closed. A horizontal or vertical constraint of the original line goes to each half. Dimensions and other constraints stay on the old ends.
How it differs from trim
Trim removes a piece. Break removes nothing — it splits one entity into two, leaving both where they were. Visually nothing changes after a break: the line looks exactly as before.
It is easy to check — click one half: only that half gets selected.