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/*
 * Copyright (c) 2012 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD-3-Clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.runtime.tree;

import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.misc.Interval;
import org.antlr.v4.runtime.misc.NotNull;

/** A tree that knows about an interval in a token stream
 *  is some kind of syntax tree. Subinterfaces distinguish
 *  between parse trees and other kinds of syntax trees we might want to create.
 */
public interface SyntaxTree extends Tree {
	/**
	 * Return an {@link Interval} indicating the index in the
	 * {@link TokenStream} of the first and last token associated with this
	 * subtree. If this node is a leaf, then the interval represents a single
	 * token and has interval i..i for token index i.
	 *
	 * An interval of i..i-1 indicates an empty interval at position
	 * i in the input stream, where 0 <= i <= the size of the input
	 * token stream.  Currently, the code base can only have i=0..n-1 but
	 * in concept one could have an empty interval after EOF. 
	 *
	 * If source interval is unknown, this returns {@link Interval#INVALID}.
	 *
	 * As a weird special case, the source interval for rules matched after
	 * EOF is unspecified.
	 */
	@NotNull
	Interval getSourceInterval();
}