# init(x:y:domain:function:) Creates a mark that fills the area between zero and the given function. ``` nonisolated init(x: Text, y: Text, domain: ClosedRange? = nil, function: @escaping @Sendable (Double) -> Double) ``` ## Discussion Parameters: - x: The localized string key for the x label. - y: The localized string key for the y label. - domain: The domain of x. If set to `nil`, the domain of the chart’s x scale will be used. - function: The function to graph.. > Note: For x values where the function is undefined or is infinity, the function is expected to return `Double.nan` or `Double.infinity` respectively. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)