Conductors: hops where wires cross (PR #1200, pending)

New section 9: the project setting that draws an arc where two wires
cross without being connected (issue #436), its three choices, which
crossings hop, and what it does not change (DXF export, the data).
Carries a pending notice until PR #1200 merges.

_Sidebar.md

@@ -22,7 +22,7 @@
 <details open>
 <summary><b>Guides</b></summary>
 
-**[Conductors](conductors)** — wire properties, what feeds which export, and cables
+**[Conductors](conductors)** — wire properties, what feeds which export, cables, and hops where wires cross
 
 **[Printing and exporting](printing_and_export)** — paper, PDF, images, and what each path does differently
 

conductors.md

@@ -291,6 +291,66 @@ Both are per project, and both are toggles you can leave off.
 
 ---
 
+## 9. Hops where wires cross
+
+> **Status: pending.** This section describes
+> [PR #1200](https://github.com/qelectrotech/qelectrotech-source-mirror/pull/1200),
+> not yet merged. Nothing here works until that lands — check the PR before
+> trying any of this against your own build. This notice will come out once
+> it merges.
+
+Where two wires cross without being connected, a project can draw a small
+arc — a **hop** — on one of them, so the crossing cannot be read as a
+connection. Until now the only way to show this was to insert a jump symbol
+and split the wire around it ([#436](https://github.com/qelectrotech/qelectrotech-source-mirror/issues/436)).
+
+![Left: the default, crossings drawn as plain lines. Right: with hops on horizontal wires, each horizontal wire arcs over the vertical ones it crosses, and the corner where the lower wire turns has no hop.](https://raw.githubusercontent.com/wiki/qelectrotech/qelectrotech-source-mirror/images/conductors-wire-hops.png)
+
+**It is off by default.** Many drawing conventions, the French one among
+them, do not use hops; a project that never turns them on is drawn and saved
+exactly as before.
+
+### Turning hops on
+
+**Projet → Propriétés du projet** (*Project properties*), page **Général**,
+the **Croisements de conducteurs** (*wire crossings*) list at the bottom:
+
+![The Croisements de conducteurs list in the project properties, set to Saut sur les conducteurs horizontaux.](https://raw.githubusercontent.com/wiki/qelectrotech/qelectrotech-source-mirror/images/conductors-wire-hops-setting.png)
+
+| Choice | What is drawn |
+|---|---|
+| **Sans saut** (*no hop*) — the default | crossings as plain lines |
+| **Saut sur les conducteurs horizontaux** | the horizontal wire arcs **over** the vertical one |
+| **Saut sur les conducteurs verticaux** | the vertical wire arcs **to the right of** the horizontal one |
+
+You choose the orientation rather than "whichever wire was drawn last", so
+the whole project looks consistent. The setting belongs to the project: it
+is saved in the `.qet` file and every folio follows it, on any computer.
+
+### Which crossings hop
+
+- Only a real **crossing** hops: one wire passing straight through another.
+- A wire that **ends** on another one (a T, usually with a junction dot), or
+  **turns** on it, is a connection, not a crossing, and never hops.
+- A crossing too close to a bend or to the end of a wire for the arc to fit
+  is drawn as a plain crossing.
+- Of two crossings closer together than one arc, only the first hops.
+
+### What it changes, and what it does not
+
+- **Drawing only.** No element is added and no wire is split: the wire
+  numbers, the wiring list, the parts list and the project database are
+  exactly the same with or without hops.
+- **Exports:** PDF, SVG, image export and printing all show the hops.
+  **DXF export does not** — it writes the wire segments itself and draws
+  crossings as plain lines.
+- **In the file:** a project with hops on carries
+  `<wire_crossings hop="horizontal"/>` (or `"vertical"`). Without that
+  element, or with any other value, no hop is drawn — so an older version of
+  QElectroTech simply shows plain crossings.
+
+---
+
 ## See also
 
 - **[User manual](user_manual)** — the walkthrough for drawing wires