What happens if a holiday falls on my leave?
A public holiday falling inside a booked leave period should not consume a leave day, since the office was closed anyway. The boundary case is common enough to be worth settling in writing, because the two records are maintained separately and neither adjusts the other by itself.
The case arrives every year and surprises somebody every year, usually in the week after a long break.
A holiday applies to everybody and costs nobody an allowance. A leave day costs one person a day. Where the two overlap, charging the day means the person paid for a closure.
The reason it needs writing down is that the records do not talk to each other. The calendar is company-wide; the request is individual.
Whoever agrees a request spanning a holiday is the one who spots it. That is a person doing a check, so the rule has to be somewhere they can read it.
Publishing the calendar early is what makes the check possible at all. A reviewer who cannot see next March's dates cannot notice that a booking crosses one.
A weekend holiday raises its own small question, and the description field is where the answer goes. Whether the day moves to a working day is decided when the entry is added, not when somebody asks.
Put both rules in the leave policy, next to the half-day rule. All three only surface when somebody is already annoyed, which is the worst moment to be writing them.
A holiday confirmed after somebody booked leave across it is the awkward version. The booking was correct when it was made, and the fairest handling is usually the same as the planned case.
Write the rule into the leave policy next to the half-day rule. Both are boundary cases that only surface when somebody is already annoyed.
Related questions
Does the product adjust the count?
The holiday calendar and the leave request are separate records. The rule for the overlap is the employer's, and it is applied when the request is reviewed.
What about a holiday on a weekend?
Whether a weekend holiday moves to a working day is a decision for the calendar, made when the entry is added. The description field is where that gets noted.
Who should spot the overlap?
Whoever reviews the request, since they see both the dates and the calendar. That is a reason to keep the calendar published well ahead.