Added the ImageWidth enumeration to the Website library target.

Services/Website/Sources/Library/Internal/Enumerations/ImageWidth.swift

@@ -0,0 +1,29 @@
+/// A rendition an image asset is available at, from the narrowest up to the full-size file.
+///
+/// ``StaticFile`` names one file per rendition, and a page's `srcset` offers them all so the browser picks by rendered width.
+/// The declaration order is the `srcset` order: narrowest first.
+enum ImageWidth: CaseIterable {
+    /// The small rendition, 480 pixels wide.
+    case small
+    /// The medium rendition, 800 pixels wide.
+    case medium
+    /// The large rendition: the full-size file, 1200 pixels wide.
+    case large
+}
+
+// MARK: - Extensions
+
+extension ImageWidth {
+
+    // MARK: Computed
+
+    /// The rendition's width in pixels: what the file is resampled to, and what its `srcset` descriptor states.
+    var width: Int {
+        switch self {
+        case .small: 480
+        case .medium: 800
+        case .large: 1200
+        }
+    }
+
+}

Services/Website/Sources/Library/Internal/Types/StaticFile.swift

@@ -14,18 +14,26 @@ struct StaticFile: Asset {
     /// The file's name, without extension.
     let fileName: String
 
+    /// The folder holding the file, or `nil` when it sits in its extensions' own folders.
+    ///
+    /// Imagery sits in a folder per page — `img/index`, `img/about` — rather than in its extension's own.
+    let folder: String?
+
     // MARK: Initializers
 
     /// Declares a static file.
     /// - Parameters:
     ///   - fileName: the file's name, without extension.
+    ///   - folder: the folder holding the file, or `nil` (the default) to use each extension's own folder.
     ///   - fileExtensions: the extensions the file is available with, one file each.
     init(
         _ fileName: String,
+        in folder: String? = nil,
         as fileExtensions: AssetExtension...
     ) {
         self.fileExtensions = fileExtensions
         self.fileName = fileName
+        self.folder = folder
     }
 
 }
@@ -55,6 +63,37 @@ extension StaticFile {
 
 }
 
+// MARK: - Methods
+
+extension StaticFile {
+
+    /// The `srcset` value offering every rendition of a responsive image, narrowest first, ending on the full-size file.
+    ///
+    /// The renditions are named by the given closure, which conventionally gives the `large` one the bare file name and the narrower ones their
+    /// width — as `srcset` files are usually named:
+    ///
+    /// ```swift
+    /// static func portrait(_ width: ImageWidth) -> Self {
+    ///     Self(width == .large ? "portrait" : "portrait-\(width.width)", in: "img/about", as: .jpg, .webp)
+    /// }
+    /// ```
+    /// - Parameters:
+    ///   - fileExtension: the format the renditions are named in.
+    ///   - version: the version token appended to each URL, or `nil` (the default) to leave them unversioned.
+    ///   - rendition: the file naming a given width.
+    /// - Returns: the `srcset` value for that format.
+    static func srcSet(
+        for fileExtension: AssetExtension,
+        version: String? = nil,
+        rendition: (ImageWidth) -> Self
+    ) -> String {
+        ImageWidth.allCases
+            .map { "\(rendition($0).urlPath(for: fileExtension, version: version)) \($0.width)w" }
+            .joined(separator: ", ")
+    }
+
+}
+
 // MARK: - Constants
 
 extension StaticFile {