---
id: R4.a
family: GR-VAL
level: core
profiles: [storage-api]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-val/r4-a
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# R4.a — An exposed workflow port must be named in the permitted alphabet

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

An exposure name is a caller-facing parameter name. Restricting it to a small alphabet keeps it usable as a key in every context a caller passes it through.

## The rule

> **Normative.** This is the rule.
>
> 1. A workflow exposure entry's `name` must match `^[a-z0-9_-]+$`.
>
> 2. A name that is absent, empty or outside that alphabet is refused with `R4_NAME_FORMAT` at `schema.{side}.{index}`, where `{side}` is `input` or `output` and `{index}` the entry's position in that side's list.
>
> 3. Unlike R4.c, this failure does not skip the entry's remaining checks: uniqueness, node existence and port declaration are all still evaluated, so two entries with no name at all yield two `R4_NAME_FORMAT` errors and one `R4_NAME_DUPLICATE` on the empty name.

## Related rules

- Names: R4.b, R4.c, R4.e
- Referenced by: R4.b, R4.c, R4.d, R4.e

---

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.