[NTG-context] underbrace label across two lines

Hi list, Following on from Aditya's solution to my previous question, I have run into a separate issue and would appreciate any assistance. Sometimes text under the underbrace can become quite long, and should be split into two (or more) lines. In the example below, "firstline" should be the top line of the underbrace label, and "secondline" should be on the lower line of the underbrace label, but as it stands, both are printed on the same line. \underbrace[mindepth=0.5cm]{\tf x+y+z}_{\vrule width 0pt height 0.5cm\relax\text{firstline secondline}} I have tried using \\ and \crlf, but to no avail. Any help would be greatly appreciated! Dean