In addition to the list, numeric, and string widget, there are widgets for entering file names, tic labels, and data ranges. This widget set is a quirky and behaves slightly differently from typical X Windows widget sets. But once you get the hang of it, the GUI is pretty handy. The last line of this buffer contains four buttons. There are various types of widgets for entering different kinds of arguments.
Numerical arguments use widgets which only accept numerical values.
There is even a special widget for inserting arrays of user-defined tic labels. There are some shortcomings of this system. Arguments which are comma separated pairs or triplets of numbers are not yet supported. An example of this is set arrow from 0,0 to 10,10 Arguments which are colon separated numbers are not yet supported. The GUI does not know how to deal with continuation lines.