What triggers it. Flowchart click/href directives, edge IDs and edge metadata, v11 @{ shape: … } node metadata, markdown strings, unclosed delimiters that would silently drop content, or syntax: "empty_layout" when content-bearing source lays out to a 0×0 canvas with no nodes, edges, or groups.

How to fix it. For preserved Mermaid syntax, remove the directive if local rendering fidelity matters, or keep it knowing the local renderer ignores it; edits touching those lines need source-level editing rather than typed mutations. For empty_layout, inspect the warning message and verify.layout, then repair the malformed or unsupported source before accepting the artifact.

Minimal reproducer

This source triggers UNSUPPORTED_SYNTAX — checked at build time against the same engine the editor runs.

flowchart LR
  A[Start] --> B[Docs]
  click B callCallback

Open this reproducer in the editor

Run am verify diagram.mmd --json, inspect this code, and apply the smallest source or typed mutation that clears it. If it persists after two mechanical attempts, return the warning and ask for human review.

In the cloned repo, am is bun run bin/am.ts.

Machine-readable: this page as Markdown.

Back to all warning codes, or open a blank editor to try a fix.