Module codes 

Stable, machine-readable diagnostic codes.

Each constant is a permanent identifier for one class of authoring mistake. The code is rendered alongside every diagnostic and emitted as a structured field by webui build --format json, so editors, CI, and AI assistants can map an error to a deterministic fix or docs page regardless of the human-readable wording. Treat these as a stable API surface — rename only with a deliberate, documented migration.

Constants

EXCESSIVE_NESTING

Template nesting exceeds the parser’s depth limit.

INVALID_CSS

A <style> block contains malformed CSS.

INVALID_EVENT_HANDLER

An @event handler value is not a valid {handler()} expression.

INVALID_FOR_EACH

<for each> value is not of the form item in collection.

INVALID_FOR_IDENTIFIER

<for each> item or collection name uses disallowed characters.

INVALID_IF_CONDITION

<if condition> value is not a parseable expression.

INVALID_W_REF

A w-ref binding is missing its required {braces}.

MALFORMED_HTML_TAG

An HTML tag could not be parsed (missing >, stray <, …).

MISSING_FOR_EACH

<for> element is missing its required each attribute.

MISSING_IF_CONDITION

<if> element is missing its required condition attribute.

MISSING_THEME_TOKEN

A CSS token required by parser output is missing from the configured theme.

RECURSIVE_TEMPLATE

A template references itself (directly or transitively) at build time.

SCRIPTLESS_EVENT_HANDLER

A scriptless HTML component contains event bindings and needs authored JS.

UNCLOSED_HTML_TAG

An HTML element is missing its closing tag.

UNEXPECTED_CLOSING_TAG

A closing tag has no matching opening tag.

UNKNOWN_COMPONENT

A component tag has no matching registered component.

UNTERMINATED_HTML_COMMENT

An HTML comment was opened but never closed with -->.

UNTERMINATED_HTML_DECLARATION

An HTML declaration was opened but never closed with >.

UNTHEMED_TOKEN

A CSS token used only with a literal var() fallback and absent from every theme — non-fatal, but usually a typo. Severity: warning.