@uml
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.
@uml 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.