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diff --git a/xpcom/ds/Dafsa.h b/xpcom/ds/Dafsa.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_Dafsa_h
+#define mozilla_Dafsa_h
+
+#include "stdint.h"
+
+#include "mozilla/Span.h"
+#include "nsStringFwd.h"
+
+namespace mozilla {
+
+/**
+ * A deterministic acyclic finite state automaton suitable for storing static
+ * dictionaries of tagged ascii strings. Consider using this if you have a very
+ * large set of strings that need an associated enum value.
+ *
+ * Currently the string tag is limited by `make_dafsa.py` to a value of [0-4].
+ * In theory [0-15] can easily be supported.
+ *
+ * See `make_dafsa.py` for more details.
+ */
+class Dafsa {
+ public:
+  using Graph = Span<const uint8_t>;
+
+  /**
+   * Initializes the DAFSA with a binary encoding generated by `make_dafsa.py`.
+   */
+  explicit Dafsa(const Graph& aData) : mData(aData) {}
+
+  ~Dafsa() = default;
+
+  /**
+   * Searches for the given string in the DAFSA.
+   *
+   * @param aKey The string to search for.
+   * @returns kKeyNotFound if not found, otherwise the associated tag.
+   */
+  int Lookup(const nsACString& aKey) const;
+
+  static const int kKeyNotFound;
+
+ private:
+  const Graph mData;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_Dafsa_h