# `Calendrical.InvalidCompositeError`

Exception returned, or raised by `use Calendrical.Composite`, for a
configuration a composite calendar cannot keep.

### Fields

* `:reason` — what makes no composite calendar: `:no_calendars_configured`,
  `:must_be_a_list_of_dates`, `:invalid_date`,
  `:must_not_be_composite_calendars`, `:must_not_be_week_calendars`,
  `:must_take_effect_on_different_days` or `:years_must_not_go_back`.

* `:value` — the date or calendar that is the reason, or `nil`.

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*Consult [api-reference.md](api-reference.md) for complete listing*