Source: Schema.org v30.1 vocabulary. Official parentItem property definition.
What does parentItem mean?
The parent of a question, answer or item in general. Typically used for Q/A discussion threads e.g. a chain of comments with the first comment being an [[Article]] or other [[CreativeWork]]. See also [[comment]] which points from something to a comment about it.
Used on types (domainIncludes)
Expected value types (rangeIncludes)
Schema.org domainIncludes and rangeIncludes are descriptive guidance, not strict validation prohibitions. Check the official reference for updates.
Related reference
Browse all Schema.org types and properties · Google feature support status