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diff --git a/intl/components/src/DateTimePart.h b/intl/components/src/DateTimePart.h
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+++ b/intl/components/src/DateTimePart.h
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+/* 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 intl_components_DateTimePart_h_
+#define intl_components_DateTimePart_h_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "mozilla/Vector.h"
+
+namespace mozilla::intl {
+
+enum class DateTimePartType : int16_t {
+  Literal,
+  Weekday,
+  Era,
+  Year,
+  YearName,
+  RelatedYear,
+  Month,
+  Day,
+  DayPeriod,
+  Hour,
+  Minute,
+  Second,
+  FractionalSecondDigits,
+  TimeZoneName,
+  Unknown
+};
+
+enum class DateTimePartSource : int16_t { Shared, StartRange, EndRange };
+
+/**
+ * The 'Part' object defined in FormatDateTimeToParts and
+ * FormatDateTimeRangeToParts
+ *
+ * Each part consists of three properties: ||Type||, ||Value|| and ||Source||,
+ * with the ||Source|| property is set to DateTimePartSource::Shared by default.
+ * (Note: From the spec, the part from FormatDateTimeToParts doesn't have the
+ * ||Source|| property, so if the caller is FormatDateTimeToParts, it should
+ * ignore the ||Source|| property).
+ *
+ * To store DateTimePart more efficiently, it doesn't store the ||Value|| of
+ * type string in this struct. Instead, it stores the end index of the string
+ * in the buffer(which is passed to DateTimeFormat::TryFormatToParts() or
+ * can be got by calling AutoFormattedDateInterval::ToSpan()). The begin index
+ * of the ||Value|| is the mEndIndex of the previous part.
+ *
+ *  Buffer
+ *  0               i                j
+ * +---------------+---------------+---------------+
+ * | Part[0].Value | Part[1].Value | Part[2].Value | ....
+ * +---------------+---------------+---------------+
+ *
+ *     Part[0].mEndIndex is i. Part[0].Value is stored in the Buffer[0..i].
+ *     Part[1].mEndIndex is j. Part[1].Value is stored in the Buffer[i..j].
+ *
+ * See:
+ * https://tc39.es/ecma402/#sec-formatdatetimetoparts
+ * https://tc39.es/ecma402/#sec-formatdatetimerangetoparts
+ */
+struct DateTimePart {
+  DateTimePart(DateTimePartType type, size_t endIndex,
+               DateTimePartSource source)
+      : mEndIndex(endIndex), mType(type), mSource(source) {}
+
+  // See the above comments for details, mEndIndex is placed first for reducing
+  // padding.
+  size_t mEndIndex;
+  DateTimePartType mType;
+  DateTimePartSource mSource;
+};
+
+// The common parts are 'month', 'literal', 'day', 'literal', 'year', 'literal',
+// 'hour', 'literal', 'minute', 'literal', which are 10 parts, for DateTimeRange
+// the number will be doubled, so choosing 32 as the initial length to prevent
+// heap allocation.
+constexpr size_t INITIAL_DATETIME_PART_VECTOR_SIZE = 32;
+using DateTimePartVector =
+    mozilla::Vector<DateTimePart, INITIAL_DATETIME_PART_VECTOR_SIZE>;
+
+}  // namespace mozilla::intl
+#endif