IDefinedDay Interface

The `IDefinedDay` interface is used to target a specific day or a recurring pattern of days within the calendar. It serves as the base for identifying dates and applying custom visual styles to them.

You can use the `IDefinedDay` interface to customize the appearance of specific dates. By providing a `date` (which can be a single date, a string, or a recurring date pattern) and an optional `dayStyle`, you can make specific days bold, underlined, disabled, or mark them as off-days.

Property	Type	Description
date	Date \| string \| IRecurringDate	The target date. Can be a Javascript `Date` object, a date string, or an `IRecurringDate` object to target multiple days.
dayStyle?	IDayStyle	Optional styling properties to apply to the targeted date(s), such as `isOffday`, `isBold`, `isUnderlined`, `isDisabled`, or `isCircled`.