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diff --git a/Firestore/Source/Model/FSTPath.h b/Firestore/Source/Model/FSTPath.h
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+++ b/Firestore/Source/Model/FSTPath.h
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+/*
+ * Copyright 2017 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * FSTPath represents a path sequence in the Firestore database. It is composed of an ordered
+ * sequence of string segments.
+ *
+ * ## Subclassing Notes
+ *
+ * FSTPath itself is an abstract class that must be specialized by subclasses. Subclasses should
+ * implement constructors for common string-based representations of the path and also override
+ * -canonicalString which converts back to the canonical string-based representation of the path.
+ */
+@interface FSTPath <SelfType> : NSObject
+
+/** Returns the path segment of the given index. */
+- (NSString *)segmentAtIndex:(int)index;
+- (id)objectAtIndexedSubscript:(int)index;
+
+- (BOOL)isEqual:(id)path;
+- (NSComparisonResult)compare:(SelfType)other;
+
+/**
+ * Returns a new path whose segments are the current path's plus one more.
+ *
+ * @param segment The new segment to concatenate to the path.
+ * @return A new path with this path's segment plus the new one.
+ */
+- (instancetype)pathByAppendingSegment:(NSString *)segment;
+
+/**
+ * Returns a new path whose segments are the current path's plus another's.
+ *
+ * @param path The new path whose segments should be concatenated to the path.
+ * @return A new path with this path's segment plus the new ones.
+ */
+- (instancetype)pathByAppendingPath:(SelfType)path;
+
+/** Returns a new path whose segments are the same as this one's minus the first one. */
+- (instancetype)pathByRemovingFirstSegment;
+
+/** Returns a new path whose segments are the same as this one's minus the first `count`. */
+- (instancetype)pathByRemovingFirstSegments:(int)count;
+
+/** Returns a new path whose segments are the same as this one's minus the last one. */
+- (instancetype)pathByRemovingLastSegment;
+
+/** Convenience method for getting the first segment of this path. */
+- (NSString *)firstSegment;
+
+/** Convenience method for getting the last segment of this path. */
+- (NSString *)lastSegment;
+
+/** Returns true if this path is a prefix of the given path. */
+- (BOOL)isPrefixOfPath:(SelfType)other;
+
+/** Returns a standardized string representation of this path. */
+- (NSString *)canonicalString;
+
+/** The number of segments in the path. */
+@property(nonatomic, readonly) int length;
+
+/** True if the path is empty. */
+@property(nonatomic, readonly, getter=isEmpty) BOOL empty;
+
+@end
+
+/** A dot-separated path for navigating sub-objects within a document. */
+@class FSTFieldPath;
+
+@interface FSTFieldPath : FSTPath <FSTFieldPath *>
+
+/**
+ * Creates and returns a new path with the given segments. The array of segments is not copied, so
+ * one should not mutate the array once it is passed in here.
+ *
+ * @param segments The underlying array of segments for the path.
+ * @return A new instance of FSTPath.
+ */
++ (instancetype)pathWithSegments:(NSArray<NSString *> *)segments;
+
+/**
+ * Creates and returns a new path from the server formatted field-path string, where path segments
+ * are separated by a dot "." and optionally encoded using backticks.
+ *
+ * @param fieldPath A dot-separated string representing the path.
+ */
++ (instancetype)pathWithServerFormat:(NSString *)fieldPath;
+
+/** Returns a field path that represents a document key. */
++ (instancetype)keyFieldPath;
+
+/** Returns a field path that represents an empty path. */
++ (instancetype)emptyPath;
+
+/** Returns YES if this is the `FSTFieldPath.keyFieldPath` field path. */
+- (BOOL)isKeyFieldPath;
+
+@end
+
+/** A slash-separated path for navigating resources (documents and collections) within Firestore. */
+@class FSTResourcePath;
+
+@interface FSTResourcePath : FSTPath <FSTResourcePath *>
+
+/**
+ * Creates and returns a new path with the given segments. The array of segments is not copied, so
+ * one should not mutate the array once it is passed in here.
+ *
+ * @param segments The underlying array of segments for the path.
+ * @return A new instance of FSTPath.
+ */
++ (instancetype)pathWithSegments:(NSArray<NSString *> *)segments;
+
+/**
+ * Creates and returns a new path from the given resource-path string, where the path segments are
+ * separated by a slash "/".
+ *
+ * @param resourcePath A slash-separated string representing the path.
+ */
++ (instancetype)pathWithString:(NSString *)resourcePath;
+@end
+
+NS_ASSUME_NONNULL_END