---
id: LANG-2
family: GR-LANG
level: core
profiles: [storage-api, runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-lang/lang-2
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# LANG-2 — A node's expression engine must be one the implementation provides

*GR-LANG (Part I) · level: core · profiles: storage-api, runtime · added in 1.0*

## The rule

> **Normative.** This is the rule.
>
> 1. A node that embeds an expression selects its engine through the reserved `engine` parameter, whose permitted values are exactly the engine identifiers the implementation provides.
>
> 2. A workflow naming an engine outside that set is refused when it is saved and again when the parameter is resolved.
>
> 3. An unrecognised engine identifier that reaches evaluation by some other route fails before any expression is evaluated.

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.