private IEnumerable<UtokenBase> YieldIndentationLeft(UnparsableAst self, BlockIndentation blockIndentation)
{
#if DEBUG
BlockIndentation originalBlockIndentation = blockIndentation;
#endif
var utokens = YieldIndentationLeft(self, ref blockIndentation);
#if DEBUG
Debug.Assert(object.ReferenceEquals(blockIndentation, originalBlockIndentation), "unwanted change of blockIndentationParameter reference in YieldIndentationLeft");
#endif
return utokens;
}