[NTG-context] smaller-bigger fontsize

ConTeXt fontsizing has \tx to make the current font style one step smaller, then another \txx does that again. For makeing the size bigger I cannot see anything other than the series \tfa \tfb \tfc \tfd. It would however be nice to also have a similar cumulative effect here. Can there be something like "\tsmall" available to reduce the font size one step (to a certain minimum, not just \tx\tx = \txx)? And similar \tbig to enlarge the font size one step? It will make the equivalent of HTML's <small> and <big> tags easy to implement for typesetting my xml data. Or are there already such things? Hans van der Meer