This APL tree type is used to represent program parts that represent function applications. E.g., if a program contains the text f(1,2,3) than this text will be parsed towards an APLtree whose name is f and whose Arg part is a TAB representing (1,2,3). Another possibility for APL is that it represents function applications of the form f@x. Of course, in this case the argument is not a TAB, but a VAR. The name is accessed by the APL_NAM_idx index. The arguments table is accessed by the APL_ARG_idx index.