LABELSIZE textOutputs the size (width and height) of the given text if it were rendered with the LABEL command. The input may be a word or a list. The output is a two item list [width height].
You can use LABELSIZE to build other forms of LABEL, such as CENTERLABEL or VERTICALLABEL. You can also use this information to "prepare" a site for text (for example, frame it or set a background).
SETLABELFONT [[Times New Roman] -24 0 0 400 0 0 0 0 3 2 1 18]
SHOW LABELSIZE "Hello
[44 24]