learn(microflows): expression functions take positional arguments only — toString(from: $X) is a silent misparse

[MendixMau]

What changed and why (one paragraph)

Workshop feedback: a session kept writing toString(from: $Temperature) and the build broke on the from:. New section in skills/learned-microflow-patterns.md records the rule (every Mendix expression function is positional-only; the name: value shape is genuine MDL in page properties, page actions and @anchor, never inside an expression) and the mechanism: mxcli's expression grammar has no named-argument production, so label: value parses as a bare identifier divided by the value (COLON is the OQL division operator). The trap is that mxcli check --references passes it silently whenever the collapsed argument count still matches the function's arity; only an arity mismatch produces an error, and that error (E006 … got 1) never names labelled arguments as the cause. Wrong/correct pair included, plus a STOP instruction: any name: inside a function call's parentheses is a stop regardless of a clean check.

Field evidence

mxcli v0.24.0 / Mendix 11.12.1, on a scratch copy of a small PoC model:

Written	mxcli check --references
toString(from: $Temperature)	passes silently, exit 0; describe microflow round-trips the labelled form verbatim
formatDateTime($D, pattern: 'yyyy-MM-dd')	passes silently, exit 0
substring(from: $S, index: 0, length: 3)	fails with substring() expects 2 to 3 argument(s), got 1. [E006]

Not measured: real mx check / Studio Pro on the silently accepted forms (no mxbuild in the environment); the skill says so.

Checklist

• No client data (leak guard clean)
• Size cap: 2 files, +31
• Test tier T0 (doc-only; no fixture covers this section)
• Instrument rules: n/a (no bin/ change)
• Routing row: n/a (existing skill, already routed baseline)
• CHANGELOG line in the same commit
• Bug entries: n/a

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https://claude.ai/code/session_01VJgWP5vEoAsNsJYqCDMGNw

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