/*!
 * Copyright 2016 The ANTLR Project. All rights reserved.
 * Licensed under the BSD-3-Clause license. See LICENSE file in the project root for license information.
 */
import { Chunk } from './Chunk';
/**
 * Represents a placeholder tag in a tree pattern. A tag can have any of the
 * following forms.
 *
 * <ul>
 * <li>{@code expr}: An unlabeled placeholder for a parser rule {@code expr}.</li>
 * <li>{@code ID}: An unlabeled placeholder for a token of type {@code ID}.</li>
 * <li>{@code e:expr}: A labeled placeholder for a parser rule {@code expr}.</li>
 * <li>{@code id:ID}: A labeled placeholder for a token of type {@code ID}.</li>
 * </ul>
 *
 * This class does not perform any validation on the tag or label names aside
 * from ensuring that the tag is a non-null, non-empty string.
 */
export declare class TagChunk extends Chunk {
    /**
     * This is the backing field for `tag`.
     */
    private _tag;
    /**
     * This is the backing field for `label`.
     */
    private _label?;
    /**
     * Construct a new instance of {@link TagChunk} using the specified label
     * and tag.
     *
     * @param label The label for the tag. If this is {@code null}, the
     * {@link TagChunk} represents an unlabeled tag.
     * @param tag The tag, which should be the name of a parser rule or token
     * type.
     *
     * @exception IllegalArgumentException if {@code tag} is {@code null} or
     * empty.
     */
    constructor(tag: string, label?: string);
    /**
     * Get the tag for this chunk.
     *
     * @return The tag for the chunk.
     */
    readonly tag: string;
    /**
     * Get the label, if any, assigned to this chunk.
     *
     * @return The label assigned to this chunk, or {@code null} if no label is
     * assigned to the chunk.
     */
    readonly label: string | undefined;
    /**
     * This method returns a text representation of the tag chunk. Labeled tags
     * are returned in the form {@code label:tag}, and unlabeled tags are
     * returned as just the tag name.
     */
    toString(): string;
}