Which check fired; stable across versions, so hosts can filter on it.
The source element (a <transition> or state element).
A human-readable explanation, in English, naming the states involved.
Always "warning": invalid documents throw SCXMLValidationError instead.
The state the warning is about (for a transition: its source).
An authoring warning: valid SCXML that is very likely not what the author meant. Nothing is rejected;
<scxml-view>and the explorer show them.