Describe the Z row of an animation

A placed root or object now offers X, Y and Z as position rows.

- Animations says that Z is the draw order, that it takes effect at
  once, and how a blended value sorts.
- Development has the check sum 1397.

Animations.md

@@ -11,9 +11,15 @@ same ids whether play bakes that content or the edit mode resolves it), and it c
 nowhere. When a container template loses the object a row aims at, the row reads *(missing)* like
 any other whose target is gone.
 
+A placed root or object offers its position as the first rows: **X**, **Y** and **Z**. *Z* is the
+draw order (higher is on top), and the order is sorted again on every render, so a keyed *Z* moves
+the object behind or in front of others while the animation plays — a weapon that swings up can
+pass behind its character. Blended values between two keys count as they are: at *Z* 4.5 the
+object is above everything on 4 and below everything on 5.
+
 Besides the schema's own properties, a row can key what an object **declares** (#104): a
 **behavior's variables** — pick the behavior (it sits below its owner in the object list) and its
-variables are offered next to *Enabled*; a behavior offers no *X*/*Y*, so a variable named `x` is
+variables are offered next to *Enabled*; a behavior offers no *X*/*Y*/*Z*, so a variable named `x` is
 that variable — and the **parameters of the shader a sprite wears**, whether the asset wears it or
 the placed object overrides it. Shader parameters are numbers, as the `Property` node declares
 them, and keys are clamped to its min/max. A variable is written before the behaviors run, so a

Development.md

@@ -15,7 +15,7 @@ npm run build        # writes dist/ and regenerates index.html
 php tools/make-user.php <name> <password> [admin|user]        # an account; every tool signs in (see Accounts)
 php tests/php/accounts.test.php                               # the API's account rules, no server needed (CI's gate job)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1396 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1397 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result