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E-STRUCTURAL-ELEMENT-MISPLACED

A scrml-defined structural element appears outside the locus it belongs to.

Error Compile-time (BS / PA stage) SPEC §4.15 (normative)

What it means

scrml defines a small set of structural elements that look like HTML tags but are scrml-language constructs: <engine>, <match>, <errors>, <onTransition>, <onTimeout>, <onIdle>, <page>. Each has a strict owning locus — the place it's grammatical to use it. Outside that locus, the compiler emits E-STRUCTURAL-ELEMENT-MISPLACED.

Owning loci

Element	Grammatical only as…	SPEC
<onTransition>	Child of `<engine>`	§51.0.H
<onTimeout>	Child of an engine state-child	§51.0.M
<onIdle>	Child of `<engine>` (sibling of state-children; one per engine)	§51.0.R (specific code: E-IDLE-MISPLACED)
<errors>	Anywhere with a parent context that supports validity-surface rendering	§55.8
<page>	Child of `<program>` in MPA mode	§40.8
<engine> / <match>	File scope or inside an engine's composite state-child (engines may nest per §51.0.K)	§51 / §18.0

Minimal reproducer

<onTransition> at file scope, outside any engine:

<onTransition from=.A to=.B>
  ${ log("transitioned") }
</onTransition>

E-STRUCTURAL-ELEMENT-MISPLACED fires at the opener — <onTransition> outside <engine>.

<onTimeout> at file scope:

<onTimeout after=5s to=.Done/>

Same error — <onTimeout> outside an engine state-child.

How to fix

Move the element inside its owning locus. For <onTransition>, wrap it in an engine declaration. For <onTimeout>, place it inside a state-child body.
If the element shouldn't exist, delete it. Misplacement sometimes reveals dead code that was moved away from its engine during refactoring.
Check the rules-inert siblings. Inside a <match> block (§18.0.2), <onTransition> fires the more specific E-MATCH-ONTRANSITION-FORBIDDEN instead. Promote the match to an engine if you need transition effects.

Specific misplacement codes

Some elements have a dedicated misplacement code with sharper messaging:

<onIdle> inside a state-child body → E-IDLE-MISPLACED (more specific than E-STRUCTURAL-ELEMENT-MISPLACED; directs to <onTimeout> instead).
<onTransition> inside a <match> block → E-MATCH-ONTRANSITION-FORBIDDEN.
effect= attribute on a state-child inside <match> → E-MATCH-EFFECT-FORBIDDEN.

When a more specific code applies, the compiler fires that one instead of the generic E-STRUCTURAL-ELEMENT-MISPLACED.

<engine> — the canonical owner of onTransition / onTimeout / onIdle.
<match> — rules-inert; effect=/onTransition forbidden here. Promote to engine instead.
<errors> — renders the auto-synthesized validity surface; needs a parent context with validators.
E-NAME-COLLIDES-RESERVED — companion error when a user component name collides with a reserved structural-element identifier.

Specification