diff --git a/Package.swift b/Package.swift
index a58a6187..4fe0ddbe 100644
--- a/Package.swift
+++ b/Package.swift
@@ -16,6 +16,7 @@ let cmarkPackageName = ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DE
 
 let package = Package(
     name: "swift-markdown",
+    platforms: [.macOS(.v10_15)],
     products: [
         .library(
             name: "Markdown",
diff --git a/Sources/Markdown/Base/Document.swift b/Sources/Markdown/Base/Document.swift
index ab84b4db..23a0ea2c 100644
--- a/Sources/Markdown/Base/Document.swift
+++ b/Sources/Markdown/Base/Document.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 /// A markup element representing the top level of a whole document.
 ///
@@ -41,7 +43,7 @@ public extension Document {
     /// - parameter options: options for parsing Markdown text.
     /// - parameter source: an explicit source URL from which the input `string` came for marking source locations.
     ///   This need not be a file URL.
-    init(parsing string: String, source: URL? = nil, options: ParseOptions = []) {
+    init(parsing string: String, source: SourceIdentifier? = nil, options: ParseOptions = []) {
         if options.contains(.parseBlockDirectives) {
             self = BlockDirectiveParser.parse(string, source: source,
                                               options: options)
@@ -50,6 +52,7 @@ public extension Document {
         }
     }
 
+    #if canImport(Foundation)
     /// Parse a file's contents into a `Document`.
     ///
     /// - parameter file: a file URL from which to load Markdown text to parse.
@@ -63,6 +66,7 @@ public extension Document {
             self = MarkupParser.parseString(string, source: file, options: options)
         }
     }
+    #endif
 
     /// Create a document from a sequence of block markup elements.
     init(_ children: some Sequence<BlockMarkup>) {
@@ -77,7 +81,9 @@ public extension Document {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDocument(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Base/Markup.swift b/Sources/Markdown/Base/Markup.swift
index b19bb6b3..74c23a33 100644
--- a/Sources/Markdown/Base/Markup.swift
+++ b/Sources/Markdown/Base/Markup.swift
@@ -89,11 +89,13 @@ func makeMarkup(_ data: _MarkupData) -> Markup {
 /// > Note: All supported markup elements are already implemented in the framework.
 /// Use this protocol only as a generic constraint.
 public protocol Markup {
+    #if !hasFeature(Embedded)
     /// Accept a `MarkupVisitor` and call the specific visitation method for this element.
     ///
     /// - parameter visitor: The `MarkupVisitor` visiting the element.
     /// - returns: The result of the visit.
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result
+    #endif
 
     /// The data backing the markup element.
     /// > Note: This property is an implementation detail; do not use it directly.
@@ -122,7 +124,7 @@ extension Markup {
     ///
     /// - Complexity: `O(1)`
     var subtreeCount: Int {
-        return raw.markup.header.subtreeCount
+        return raw.markup.subtreeCount
     }
 
     /// Return this element without ``SoftBreak`` elements, or `nil` if this
@@ -178,7 +180,7 @@ extension Markup {
     ///
     /// - Complexity: `O(1)`
     public var childCount: Int {
-        return raw.markup.header.childCount
+        return raw.markup.childCount
     }
 
     /// `true` if this element has no children.
diff --git a/Sources/Markdown/Base/RawMarkup.swift b/Sources/Markdown/Base/RawMarkup.swift
index a4dabe20..9e803b24 100644
--- a/Sources/Markdown/Base/RawMarkup.swift
+++ b/Sources/Markdown/Base/RawMarkup.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 /// The data specific to a kind of markup element.
 ///
@@ -93,6 +95,54 @@ public struct RawMarkupHeader {
     var parsedRange: SourceRange?
 }
 
+#if hasFeature(Embedded)
+/// Embedded Swift variant: uses a plain array for children storage instead of
+/// tail-allocated ManagedBuffer elements, avoiding the self-referential generic
+/// `ManagedBuffer<RawMarkupHeader, RawMarkup>` that causes the compiler's
+/// generic specializer to hang (https://github.com/swiftlang/swift/pull/88296).
+final class RawMarkup {
+    var header: RawMarkupHeader
+    private let _children: [RawMarkup]
+
+    fileprivate static func create(data: RawMarkupData, parsedRange: SourceRange?, children: [RawMarkup]) -> RawMarkup {
+        return RawMarkup(
+            header: RawMarkupHeader(data: data,
+                                    childCount: children.count,
+                                    subtreeCount: 1 + children.subtreeCount,
+                                    parsedRange: parsedRange),
+            children: children)
+    }
+
+    private init(header: RawMarkupHeader, children: [RawMarkup]) {
+        self.header = header
+        self._children = children
+    }
+
+    var data: RawMarkupData { header.data }
+    var childCount: Int { header.childCount }
+    var subtreeCount: Int { header.subtreeCount }
+    var parsedRange: SourceRange? { header.parsedRange }
+
+    func child(at index: Int) -> RawMarkup {
+        precondition(index < header.childCount)
+        return _children[index]
+    }
+
+    func copyChildren() -> [RawMarkup] { _children }
+
+    var children: some Sequence<RawMarkup> { _children }
+
+    enum Error: Swift.Error, CustomStringConvertible {
+        case concreteConversionError(from: RawMarkup, to: Markup.Type)
+        var description: String {
+            switch self {
+            case let .concreteConversionError(raw, to: type):
+                return "Can't wrap a \(raw.data) in a \(type)"
+            }
+        }
+    }
+}
+#else
 final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
     enum Error: LocalizedError {
         case concreteConversionError(from: RawMarkup, to: Markup.Type)
@@ -103,7 +153,8 @@ final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
             }
         }
     }
-    private static func create(data: RawMarkupData, parsedRange: SourceRange?, children: [RawMarkup]) -> RawMarkup {
+
+    fileprivate static func create(data: RawMarkupData, parsedRange: SourceRange?, children: [RawMarkup]) -> RawMarkup {
         let buffer = self.create(minimumCapacity: children.count) { _ in
             RawMarkupHeader(data: data,
                             childCount: children.count,
@@ -155,10 +206,8 @@ final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
     }
 
     /// The children of this element.
-    var children: AnySequence<RawMarkup> {
-        return AnySequence((0..<childCount).lazy.map { Int -> RawMarkup in
-            self.child(at: 0)
-        })
+    var children: some Sequence<RawMarkup> {
+        return (0..<childCount).lazy.map { _ in self.child(at: 0) }
     }
 
     deinit {
@@ -166,6 +215,12 @@ final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
             $0.deinitialize(count: header.childCount)
         }
     }
+}
+#endif
+
+// MARK: - Shared API
+
+extension RawMarkup {
 
     // MARK: Aspects
 
@@ -174,11 +229,11 @@ final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
         if self === other {
             return true
         }
-        guard self.header.childCount == other.header.childCount,
-            self.header.data == other.header.data else {
+        guard self.childCount == other.childCount,
+            self.data == other.data else {
                 return false
         }
-        for i in 0..<header.childCount {
+        for i in 0..<childCount {
             guard self.child(at: i).hasSameStructure(as: other.child(at: i)) else {
                 return false
             }
@@ -197,16 +252,16 @@ final class RawMarkup: ManagedBuffer<RawMarkupHeader, RawMarkup> {
 
         let parsedRange: SourceRange?
         if preserveRange {
-            parsedRange = header.parsedRange
+            parsedRange = self.parsedRange
         } else {
-            parsedRange = newChild.header.parsedRange
+            parsedRange = newChild.parsedRange
         }
 
-        return RawMarkup.create(data: header.data, parsedRange: parsedRange, children: newChildren)
+        return RawMarkup.create(data: data, parsedRange: parsedRange, children: newChildren)
     }
 
     func withChildren<Children: Collection>(_ newChildren: Children) -> RawMarkup where Children.Element == RawMarkup {
-        return .create(data: header.data, parsedRange: header.parsedRange, children: Array(newChildren))
+        return .create(data: data, parsedRange: parsedRange, children: Array(newChildren))
     }
 
     // MARK: Block Creation
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/BlockDirective.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/BlockDirective.swift
index d7bd9827..8ef2de7d 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/BlockDirective.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/BlockDirective.swift	
@@ -174,7 +174,9 @@ public extension BlockDirective {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitBlockDirective(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/BlockQuote.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/BlockQuote.swift
index a24a72fd..ef606f65 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/BlockQuote.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/BlockQuote.swift	
@@ -41,7 +41,9 @@ public extension BlockQuote {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitBlockQuote(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/CustomBlock.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/CustomBlock.swift
index 403cf5b0..e0a297c3 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/CustomBlock.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/CustomBlock.swift	
@@ -41,7 +41,9 @@ public extension CustomBlock {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitCustomBlock(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenAbstract.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenAbstract.swift
index 96679bcd..bafd69da 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenAbstract.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenAbstract.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// A parsed Doxygen `\abstract` command.
 ///
 /// The Doxygen support in Swift-Markdown parses `\abstract` commands of the form
@@ -34,9 +32,11 @@ public struct DoxygenAbstract: BlockContainer {
         self._data = data
     }
 
+    #if !hasFeature(Embedded)
     public func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDoxygenAbstract(self)
     }
+    #endif
 }
 
 public extension DoxygenAbstract {
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenDiscussion.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenDiscussion.swift
index 6f72fdc4..b7b79f34 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenDiscussion.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenDiscussion.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// A parsed Doxygen `\discussion` command.
 ///
 /// The Doxygen support in Swift-Markdown parses `\discussion` commands of the form
@@ -34,9 +32,11 @@ public struct DoxygenDiscussion: BlockContainer {
         self._data = data
     }
 
+    #if !hasFeature(Embedded)
     public func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDoxygenDiscussion(self)
     }
+    #endif
 }
 
 public extension DoxygenDiscussion {
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenNote.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenNote.swift
index df9e5eac..efaafd9b 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenNote.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenNote.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// A parsed Doxygen `\note` command.
 ///
 /// The Doxygen support in Swift-Markdown parses `\note` commands of the form
@@ -34,9 +32,11 @@ public struct DoxygenNote: BlockContainer {
         self._data = data
     }
 
+    #if !hasFeature(Embedded)
     public func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDoxygenNote(self)
     }
+    #endif
 }
 
 public extension DoxygenNote {
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenParameter.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenParameter.swift
index 3f4df5a7..43016dd6 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenParameter.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenParameter.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// A parsed Doxygen `\param` command.
 ///
 /// The Doxygen support in Swift-Markdown parses `\param` commands of the form
@@ -37,9 +35,11 @@ public struct DoxygenParameter: BlockContainer {
         self._data = data
     }
 
+    #if !hasFeature(Embedded)
     public func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDoxygenParameter(self)
     }
+    #endif
 }
 
 public extension DoxygenParameter {
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenReturns.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenReturns.swift
index 2a014b3f..b391b8c8 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenReturns.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/Doxygen Commands/DoxygenReturns.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// A parsed Doxygen `\returns`, `\return`, or `\result` command.
 ///
 /// The Doxygen support in Swift-Markdown parses `\returns` commands of the form
@@ -34,9 +32,11 @@ public struct DoxygenReturns: BlockContainer {
         self._data = data
     }
 
+    #if !hasFeature(Embedded)
     public func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitDoxygenReturns(self)
     }
+    #endif
 }
 
 public extension DoxygenReturns {
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/ListItem.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/ListItem.swift
index 57f7b71e..3fd270b8 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/ListItem.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/ListItem.swift	
@@ -64,7 +64,9 @@ public extension ListItem {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitListItem(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/OrderedList.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/OrderedList.swift
index e52243b8..31bb006f 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/OrderedList.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/OrderedList.swift	
@@ -54,7 +54,9 @@ public extension OrderedList {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitOrderedList(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Block Container Blocks/UnorderedList.swift b/Sources/Markdown/Block Nodes/Block Container Blocks/UnorderedList.swift
index dac9ce20..b536fed7 100644
--- a/Sources/Markdown/Block Nodes/Block Container Blocks/UnorderedList.swift	
+++ b/Sources/Markdown/Block Nodes/Block Container Blocks/UnorderedList.swift	
@@ -35,7 +35,9 @@ public extension UnorderedList {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitUnorderedList(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Inline Container Blocks/Paragraph.swift b/Sources/Markdown/Block Nodes/Inline Container Blocks/Paragraph.swift
index e6614213..7ef8dbdf 100644
--- a/Sources/Markdown/Block Nodes/Inline Container Blocks/Paragraph.swift	
+++ b/Sources/Markdown/Block Nodes/Inline Container Blocks/Paragraph.swift	
@@ -41,7 +41,9 @@ public extension Paragraph {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitParagraph(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Leaf Blocks/CodeBlock.swift b/Sources/Markdown/Block Nodes/Leaf Blocks/CodeBlock.swift
index 07214fb9..3136505e 100644
--- a/Sources/Markdown/Block Nodes/Leaf Blocks/CodeBlock.swift	
+++ b/Sources/Markdown/Block Nodes/Leaf Blocks/CodeBlock.swift	
@@ -60,7 +60,9 @@ public extension CodeBlock {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitCodeBlock(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Leaf Blocks/HTMLBlock.swift b/Sources/Markdown/Block Nodes/Leaf Blocks/HTMLBlock.swift
index c41c79e7..135fe785 100644
--- a/Sources/Markdown/Block Nodes/Leaf Blocks/HTMLBlock.swift	
+++ b/Sources/Markdown/Block Nodes/Leaf Blocks/HTMLBlock.swift	
@@ -46,7 +46,9 @@ public extension HTMLBlock {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitHTMLBlock(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Leaf Blocks/Heading.swift b/Sources/Markdown/Block Nodes/Leaf Blocks/Heading.swift
index 55fe45c3..57eb9a19 100644
--- a/Sources/Markdown/Block Nodes/Leaf Blocks/Heading.swift	
+++ b/Sources/Markdown/Block Nodes/Leaf Blocks/Heading.swift	
@@ -61,7 +61,9 @@ public extension Heading {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitHeading(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Block Nodes/Leaf Blocks/ThematicBreak.swift b/Sources/Markdown/Block Nodes/Leaf Blocks/ThematicBreak.swift
index 8beeb491..4bcbdc8d 100644
--- a/Sources/Markdown/Block Nodes/Leaf Blocks/ThematicBreak.swift	
+++ b/Sources/Markdown/Block Nodes/Leaf Blocks/ThematicBreak.swift	
@@ -33,7 +33,9 @@ public extension ThematicBreak {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitThematicBreak(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Infrastructure/SourceIdentifier.swift b/Sources/Markdown/Infrastructure/SourceIdentifier.swift
new file mode 100644
index 00000000..6b246fb8
--- /dev/null
+++ b/Sources/Markdown/Infrastructure/SourceIdentifier.swift
@@ -0,0 +1,20 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+#if canImport(Foundation)
+import Foundation
+public typealias SourceIdentifier = URL
+#else
+/// Lightweight replacement for URL in Embedded Swift contexts.
+public struct SourceIdentifier: Hashable, Sendable {
+    public var path: String
+    public init(path: String) { self.path = path }
+}
+#endif
diff --git a/Sources/Markdown/Infrastructure/SourceLocation.swift b/Sources/Markdown/Infrastructure/SourceLocation.swift
index a7de4084..64bcdb71 100644
--- a/Sources/Markdown/Infrastructure/SourceLocation.swift
+++ b/Sources/Markdown/Infrastructure/SourceLocation.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 /// A location in a source file.
 public struct SourceLocation: Hashable, CustomStringConvertible, Comparable, Sendable {
@@ -29,7 +31,7 @@ public struct SourceLocation: Hashable, CustomStringConvertible, Comparable, Sen
     public var column: Int
 
     /// The source file for which this location applies, if it came from an accessible location.
-    public var source: URL?
+    public var source: SourceIdentifier?
 
     /// Create a source location with line, column, and optional source to which the location applies.
     ///
@@ -37,7 +39,7 @@ public struct SourceLocation: Hashable, CustomStringConvertible, Comparable, Sen
     /// - parameter column: The column of the location, starting with 1.
     /// - parameter source: The URL in which the location resides, or `nil` if there is not a specific
     ///   file or resource that needs to be identified.
-    public init(line: Int, column: Int, source: URL?) {
+    public init(line: Int, column: Int, source: SourceIdentifier?) {
         self.line = line
         self.column = column
         self.source = source
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/Emphasis.swift b/Sources/Markdown/Inline Nodes/Inline Containers/Emphasis.swift
index 4b28f51e..813e35a1 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/Emphasis.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/Emphasis.swift	
@@ -50,7 +50,9 @@ public extension Emphasis {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitEmphasis(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/Image.swift b/Sources/Markdown/Inline Nodes/Inline Containers/Image.swift
index cde5bf03..3eed62ca 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/Image.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/Image.swift	
@@ -95,7 +95,9 @@ public extension Image {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitImage(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/InlineAttributes.swift b/Sources/Markdown/Inline Nodes/Inline Containers/InlineAttributes.swift
index 5cffe1ff..3fa178fb 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/InlineAttributes.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/InlineAttributes.swift	
@@ -53,7 +53,9 @@ public extension InlineAttributes {
     
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitInlineAttributes(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/Link.swift b/Sources/Markdown/Inline Nodes/Inline Containers/Link.swift
index e1143626..03fba0ac 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/Link.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/Link.swift	
@@ -98,7 +98,9 @@ public extension Link {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitLink(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/Strikethrough.swift b/Sources/Markdown/Inline Nodes/Inline Containers/Strikethrough.swift
index 7d5d0b11..3ff529c9 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/Strikethrough.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/Strikethrough.swift	
@@ -49,7 +49,9 @@ public extension Strikethrough {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitStrikethrough(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Containers/Strong.swift b/Sources/Markdown/Inline Nodes/Inline Containers/Strong.swift
index d72d8550..fe61bfff 100644
--- a/Sources/Markdown/Inline Nodes/Inline Containers/Strong.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Containers/Strong.swift	
@@ -49,7 +49,9 @@ public extension Strong {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitStrong(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/CustomInline.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/CustomInline.swift
index 0505bb93..8ed63c2f 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/CustomInline.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/CustomInline.swift	
@@ -48,7 +48,9 @@ public extension CustomInline {
         return text
     }
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitCustomInline(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/InlineCode.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/InlineCode.swift
index c0000131..1f2337f4 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/InlineCode.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/InlineCode.swift	
@@ -54,7 +54,9 @@ public extension InlineCode {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitInlineCode(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/InlineHTML.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/InlineHTML.swift
index 90334649..00aa425b 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/InlineHTML.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/InlineHTML.swift	
@@ -52,7 +52,9 @@ public extension InlineHTML {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitInlineHTML(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/LineBreak.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/LineBreak.swift
index 60b5cfcb..6f456a83 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/LineBreak.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/LineBreak.swift	
@@ -41,7 +41,9 @@ public extension LineBreak {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitLineBreak(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/SoftBreak.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/SoftBreak.swift
index 12774bc5..62010101 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/SoftBreak.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/SoftBreak.swift	
@@ -41,7 +41,9 @@ public extension SoftBreak {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitSoftBreak(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/SymbolLink.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/SymbolLink.swift
index 586652e2..000e145d 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/SymbolLink.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/SymbolLink.swift	
@@ -59,9 +59,11 @@ public extension SymbolLink {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitSymbolLink(self)
     }
+    #endif
 
     // MARK: PlainTextConvertibleMarkup
 
diff --git a/Sources/Markdown/Inline Nodes/Inline Leaves/Text.swift b/Sources/Markdown/Inline Nodes/Inline Leaves/Text.swift
index 7b90a660..f8a4b6c8 100644
--- a/Sources/Markdown/Inline Nodes/Inline Leaves/Text.swift	
+++ b/Sources/Markdown/Inline Nodes/Inline Leaves/Text.swift	
@@ -53,7 +53,9 @@ public extension Text {
 
     // MARK: Visitation
 
+    #if !hasFeature(Embedded)
     func accept<V: MarkupVisitor>(_ visitor: inout V) -> V.Result {
         return visitor.visitText(self)
     }
+    #endif
 }
diff --git a/Sources/Markdown/Interpretive Nodes/Aside.swift b/Sources/Markdown/Interpretive Nodes/Aside.swift
index a01a7a05..92e12a9a 100644
--- a/Sources/Markdown/Interpretive Nodes/Aside.swift	
+++ b/Sources/Markdown/Interpretive Nodes/Aside.swift	
@@ -8,8 +8,6 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-import Foundation
-
 /// An auxiliary aside element interpreted from a block quote.
 ///
 /// Asides are written as a block quote starting with a special plain-text tag,
diff --git a/Sources/Markdown/Parser/BlockDirectiveParser.swift b/Sources/Markdown/Parser/BlockDirectiveParser.swift
index c22f003b..c35c1189 100644
--- a/Sources/Markdown/Parser/BlockDirectiveParser.swift
+++ b/Sources/Markdown/Parser/BlockDirectiveParser.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 struct PendingBlockDirective {
     enum ParseState {
@@ -299,7 +301,7 @@ struct TrimmedLine {
 
     /// The source file or resource from which the line came,
     /// or `nil` if no such file or resource can be identified.
-    let source: URL?
+    let source: SourceIdentifier?
 
     /// `true` if this line is empty or consists of all space `" "` or tab
     /// `"\t"` characters.
@@ -314,7 +316,7 @@ struct TrimmedLine {
     ///   - source: The source file or resource from which the line came, or `nil` if no such file or resource can be identified.
     ///   - lineNumber: The line number of this line in the source if known, starting with `0`.
     ///   - parseIndex: The current index a parser is looking at on a line, or `nil` if a parser is looking at the start of the untrimmed text.
-    init(_ untrimmedText: Substring, source: URL?, lineNumber: Int?, parseIndex: Substring.Index? = nil) {
+    init(_ untrimmedText: Substring, source: SourceIdentifier?, lineNumber: Int?, parseIndex: Substring.Index? = nil) {
         self.untrimmedText = untrimmedText
         self.source = source
         self.parseIndex = parseIndex ?? untrimmedText.startIndex
@@ -1132,7 +1134,7 @@ extension Document {
     /// Convert a ``ParseContainer` to a ``Document``.
     ///
     /// - Precondition: The `rootContainer` must be the `.root` case.
-    fileprivate init(converting rootContainer: ParseContainer, from source: URL?,
+    fileprivate init(converting rootContainer: ParseContainer, from source: SourceIdentifier?,
                      options: ParseOptions) {
         guard case .root = rootContainer else {
             fatalError("Tried to convert a non-root container to a `Document`")
@@ -1156,13 +1158,15 @@ extension Document {
 }
 
 struct BlockDirectiveParser {
+    #if canImport(Foundation)
     static func parse(_ input: URL, options: ParseOptions = []) throws -> Document {
         let string = try String(contentsOf: input, encoding: .utf8)
         return parse(string, source: input, options: options)
     }
+    #endif
 
     /// Parse the input.
-    static func parse(_ input: String, source: URL?,
+    static func parse(_ input: String, source: SourceIdentifier?,
                       options: ParseOptions = []) -> Document {
         // Phase 0: Split the input into lines lazily, keeping track of
         // line numbers, consecutive blank lines, and start positions on each line where indentation ends.
diff --git a/Sources/Markdown/Parser/CommonMarkConverter.swift b/Sources/Markdown/Parser/CommonMarkConverter.swift
index 510bbfda..d0152e38 100644
--- a/Sources/Markdown/Parser/CommonMarkConverter.swift
+++ b/Sources/Markdown/Parser/CommonMarkConverter.swift
@@ -10,7 +10,9 @@
 
 import cmark_gfm
 import cmark_gfm_extensions
+#if canImport(Foundation)
 import Foundation
+#endif
 
 /// String-based CommonMark node type identifiers.
 ///
@@ -82,7 +84,7 @@ fileprivate struct MarkupConverterState {
         var range: SourceRange?
     }
     /// The original source whose conversion created this state.
-    let source: URL?
+    let source: SourceIdentifier?
 
     /// An opaque pointer to a `cmark_iter` used during parsing.
     let iterator: UnsafeMutablePointer<cmark_iter>?
@@ -99,7 +101,7 @@ fileprivate struct MarkupConverterState {
     private(set) var headerSeen: Bool
     private(set) var pendingTableBody: PendingTableBody?
 
-    init(source: URL?, iterator: UnsafeMutablePointer<cmark_iter>?, event: cmark_event_type, node: UnsafeMutablePointer<cmark_node>?, options: ParseOptions, headerSeen: Bool, pendingTableBody: PendingTableBody?) {
+    init(source: SourceIdentifier?, iterator: UnsafeMutablePointer<cmark_iter>?, event: cmark_event_type, node: UnsafeMutablePointer<cmark_node>?, options: ParseOptions, headerSeen: Bool, pendingTableBody: PendingTableBody?) {
         self.source = source
         self.iterator = iterator
         self.event = event
@@ -608,7 +610,7 @@ struct MarkupParser {
         return MarkupConversion(state: childConversion.state.next(), result: .inlineAttributes(attributes: attributes, parsedRange: parsedRange, childConversion.result))
      }
 
-    static func parseString(_ string: String, source: URL?, options: ParseOptions) -> Document {
+    static func parseString(_ string: String, source: SourceIdentifier?, options: ParseOptions) -> Document {
         cmark_gfm_core_extensions_ensure_registered()
 
         var cmarkOptions = CMARK_OPT_TABLE_SPANS
diff --git a/Sources/Markdown/Parser/LazySplitLines.swift b/Sources/Markdown/Parser/LazySplitLines.swift
index 398cda89..f353cf66 100644
--- a/Sources/Markdown/Parser/LazySplitLines.swift
+++ b/Sources/Markdown/Parser/LazySplitLines.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 /// A lazy sequence of split lines that keeps track of initial indentation and
 /// consecutive runs of empty lines.
@@ -25,9 +27,9 @@ struct LazySplitLines: Sequence {
 
         /// The source file or resource from which the line came,
         /// or `nil` if no such file or resource can be identified.
-        private var source: URL?
+        private var source: SourceIdentifier?
 
-        init<S: StringProtocol>(_ input: S, source: URL?) where S.SubSequence == Substring {
+        init<S: StringProtocol>(_ input: S, source: SourceIdentifier?) where S.SubSequence == Substring {
             self.rawLines = input.split(omittingEmptySubsequences: false, whereSeparator: \.isNewline)
             self.index = rawLines.startIndex
             self.source = source
@@ -57,9 +59,9 @@ struct LazySplitLines: Sequence {
 
     /// The source file or resource from which the line came,
     /// or `nil` if no such file or resource can be identified.
-    private let source: URL?
+    private let source: SourceIdentifier?
 
-    init(_ input: Substring, source: URL?) {
+    init(_ input: Substring, source: SourceIdentifier?) {
         self.input = input
         self.source = source
     }
diff --git a/Sources/Markdown/Parser/RangeAdjuster.swift b/Sources/Markdown/Parser/RangeAdjuster.swift
index 88ab0e58..00190521 100644
--- a/Sources/Markdown/Parser/RangeAdjuster.swift
+++ b/Sources/Markdown/Parser/RangeAdjuster.swift
@@ -43,7 +43,11 @@ struct RangeAdjuster: MarkupWalker {
         markup.raw.markup.header.parsedRange = adjustedRange
 
         for child in markup.children {
+            #if hasFeature(Embedded)
+            visit(child)
+            #else
             child.accept(&self)
+            #endif
         }
 
         // End unsafe stuff.
diff --git a/Sources/Markdown/Visitor/MarkupVisitor.swift b/Sources/Markdown/Visitor/MarkupVisitor.swift
index 9c3e38a7..df2bba85 100644
--- a/Sources/Markdown/Visitor/MarkupVisitor.swift
+++ b/Sources/Markdown/Visitor/MarkupVisitor.swift
@@ -317,12 +317,56 @@ public protocol MarkupVisitor<Result> {
 }
 
 extension MarkupVisitor {
+    #if hasFeature(Embedded)
+    // Embedded Swift cannot call generic methods on existentials, so we use
+    // enum-based dispatch instead of the accept<V> virtual dispatch pattern.
+    public mutating func visit(_ markup: Markup) -> Result {
+        switch markup._data.raw.markup.data {
+        case .blockQuote: return visitBlockQuote(BlockQuote(markup._data))
+        case .codeBlock: return visitCodeBlock(CodeBlock(markup._data))
+        case .customBlock: return visitCustomBlock(CustomBlock(markup._data))
+        case .document: return visitDocument(Document(markup._data))
+        case .heading: return visitHeading(Heading(markup._data))
+        case .thematicBreak: return visitThematicBreak(ThematicBreak(markup._data))
+        case .htmlBlock: return visitHTMLBlock(HTMLBlock(markup._data))
+        case .listItem: return visitListItem(ListItem(markup._data))
+        case .orderedList: return visitOrderedList(OrderedList(markup._data))
+        case .unorderedList: return visitUnorderedList(UnorderedList(markup._data))
+        case .paragraph: return visitParagraph(Paragraph(markup._data))
+        case .blockDirective: return visitBlockDirective(BlockDirective(markup._data))
+        case .inlineCode: return visitInlineCode(InlineCode(markup._data))
+        case .customInline: return visitCustomInline(CustomInline(markup._data))
+        case .emphasis: return visitEmphasis(Emphasis(markup._data))
+        case .image: return visitImage(Image(markup._data))
+        case .inlineHTML: return visitInlineHTML(InlineHTML(markup._data))
+        case .lineBreak: return visitLineBreak(LineBreak(markup._data))
+        case .link: return visitLink(Link(markup._data))
+        case .softBreak: return visitSoftBreak(SoftBreak(markup._data))
+        case .strong: return visitStrong(Strong(markup._data))
+        case .text: return visitText(Text(markup._data))
+        case .symbolLink: return visitSymbolLink(SymbolLink(markup._data))
+        case .inlineAttributes: return visitInlineAttributes(InlineAttributes(markup._data))
+        case .strikethrough: return visitStrikethrough(Strikethrough(markup._data))
+        case .table: return visitTable(Table(markup._data))
+        case .tableHead: return visitTableHead(Table.Head(markup._data))
+        case .tableBody: return visitTableBody(Table.Body(markup._data))
+        case .tableRow: return visitTableRow(Table.Row(markup._data))
+        case .tableCell: return visitTableCell(Table.Cell(markup._data))
+        case .doxygenDiscussion: return visitDoxygenDiscussion(DoxygenDiscussion(markup._data))
+        case .doxygenNote: return visitDoxygenNote(DoxygenNote(markup._data))
+        case .doxygenAbstract: return visitDoxygenAbstract(DoxygenAbstract(markup._data))
+        case .doxygenParam: return visitDoxygenParameter(DoxygenParameter(markup._data))
+        case .doxygenReturns: return visitDoxygenReturns(DoxygenReturns(markup._data))
+        }
+    }
+    #else
     // Default implementation: call `accept` on the markup element,
     // dispatching into each leaf element's implementation, which then
     // dispatches to the correct visit___ method.
     public mutating func visit(_ markup: Markup) -> Result {
         return markup.accept(&self)
     }
+    #endif
     public mutating func visitBlockQuote(_ blockQuote: BlockQuote) -> Result {
         return defaultVisit(blockQuote)
     }
diff --git a/Sources/Markdown/Walker/Walkers/HTMLFormatter.swift b/Sources/Markdown/Walker/Walkers/HTMLFormatter.swift
index ab047c94..25c1f372 100644
--- a/Sources/Markdown/Walker/Walkers/HTMLFormatter.swift
+++ b/Sources/Markdown/Walker/Walkers/HTMLFormatter.swift
@@ -8,7 +8,23 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
+
+fileprivate extension String {
+    func _replacingOccurrences(of target: Character, with replacement: String) -> String {
+        var result = ""
+        for char in self {
+            if char == target {
+                result += replacement
+            } else {
+                result.append(char)
+            }
+        }
+        return result
+    }
+}
 
 /// Options given to the ``HTMLFormatter``.
 public struct HTMLFormatterOptions: OptionSet {
@@ -286,8 +302,9 @@ public struct HTMLFormatter: MarkupWalker {
     }
 
     public mutating func visitInlineAttributes(_ attributes: InlineAttributes) -> () {
-        result += "<span data-attributes=\"\(attributes.attributes.replacingOccurrences(of: "\"", with: "\\\""))\""
+        result += "<span data-attributes=\"\(attributes.attributes._replacingOccurrences(of: "\"" as Character, with: "\\\""))\""
 
+        #if canImport(Foundation)
         let wrappedAttributes = "{\(attributes.attributes)}"
         if options.contains(.parseInlineAttributeClass),
            let attributesData = wrappedAttributes.data(using: .utf8)
@@ -315,6 +332,7 @@ public struct HTMLFormatter: MarkupWalker {
                 result += " class=\"\(parsedAttributes.class)\""
             }
         }
+        #endif
 
         result += ">"
         descendInto(attributes)
diff --git a/Sources/Markdown/Walker/Walkers/MarkupFormatter.swift b/Sources/Markdown/Walker/Walkers/MarkupFormatter.swift
index 99f24ed4..bbcc21f2 100644
--- a/Sources/Markdown/Walker/Walkers/MarkupFormatter.swift
+++ b/Sources/Markdown/Walker/Walkers/MarkupFormatter.swift
@@ -8,7 +8,9 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 fileprivate extension Markup {
     /// The parental chain of elements from a root to this element.
@@ -596,7 +598,7 @@ public struct MarkupFormatter: MarkupWalker {
             return
         }
 
-        let words = string.components(separatedBy: CharacterSet(charactersIn: " \t"))[...]
+        let words = string.split(omittingEmptySubsequences: false, whereSeparator: { $0 == " " || $0 == "\t" }).map(String.init)[...]
 
         /// Hard line breaks in Markdown require two spaces before the newline; soft breaks require none.
         let breakSuffix: String
diff --git a/Sources/Markdown/Walker/Walkers/MarkupTreeDumper.swift b/Sources/Markdown/Walker/Walkers/MarkupTreeDumper.swift
index 0b588741..8d934fee 100644
--- a/Sources/Markdown/Walker/Walkers/MarkupTreeDumper.swift
+++ b/Sources/Markdown/Walker/Walkers/MarkupTreeDumper.swift
@@ -8,12 +8,27 @@
  See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+#if canImport(Foundation)
 import Foundation
+#endif
 
 fileprivate extension String {
-    /// A version of `self` with newline "\n" characters escaped as "\\n".
     var newlineEscaped: String {
-        return replacingOccurrences(of: "\n", with: "\\n")
+        var result = ""
+        for char in self {
+            if char == "\n" {
+                result += "\\n"
+            } else {
+                result.append(char)
+            }
+        }
+        return result
+    }
+
+    func _trimmingWhitespace() -> String {
+        guard let start = firstIndex(where: { $0 != " " && $0 != "\t" }),
+              let end = lastIndex(where: { $0 != " " && $0 != "\t" }) else { return "" }
+        return String(self[start...end])
     }
 }
 
@@ -275,7 +290,7 @@ struct MarkupTreeDumper: MarkupWalker {
         if tableCell.rowspan != 1 {
             desc += " rowspan: \(tableCell.rowspan)"
         }
-        desc = desc.trimmingCharacters(in: .whitespaces)
+        desc = desc._trimmingWhitespace()
         if !desc.isEmpty {
             dump(tableCell, customDescription: desc)
         } else {