Calendar parent ID.

Holiday calendars can have parent-child relationships, creating a hierarchy. Child calendars inherit holidays from their parent calendars.

Common use case: Country → State → City hierarchy

Example:

• Brazil (parent)
  • São Paulo (child of Brazil)
    • Campinas (child of São Paulo)

When you query holidays for Campinas, you automatically get:

• Campinas city holidays
• São Paulo state holidays
• Brazil national holidays

You can reference the parent calendar using either:

• parent_id: The internal parent calendar ID
• parent_external_id: The parent calendar external_id