Animations: behavior variables and shader parameters as row targets (#104)

Animations.md

@@ -11,6 +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.
 
+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
+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
+graph reads this frame's value. When the behavior is removed, the variable renamed or the shader
+swapped for one without the parameter, the row reads *(missing)* and keeps its keys.
+
 Its two properties are **Frames per second** (default 10) and **Playback**: *Loop*, *Once (hold)*
 (ends on the last value and leaves it), *Once (reset)* (ends and puts back what every target held
 before the start) or *Ping-pong*. The last key over all rows decides how long one pass lasts — the