function requireConstants () {
	if (hasRequiredConstants) return constants$3;
	hasRequiredConstants = 1;
	// Note: this is the semver.org version of the spec that it implements
	// Not necessarily the package version of this code.
	const SEMVER_SPEC_VERSION = '2.0.0';

	const MAX_LENGTH = 256;
	const MAX_SAFE_INTEGER = Number.MAX_SAFE_INTEGER ||
	/* istanbul ignore next */ 9007199254740991;

	// Max safe segment length for coercion.
	const MAX_SAFE_COMPONENT_LENGTH = 16;

	constants$3 = {
	  SEMVER_SPEC_VERSION,
	  MAX_LENGTH,
	  MAX_SAFE_INTEGER,
	  MAX_SAFE_COMPONENT_LENGTH,
	};
	return constants$3;
}
Initialize internal header tracking properties on a request instance.

@param {Object} req the instance
@api private