query_text_extents(+Fontable, +String, -Lbearing, -RBearing,
                        -Width, -Ascent, -Descent)
     query_text_extents(+Fontable, +String, -Lbearing, -RBearing,
                        -Width, -Ascent, -Descent, -Attribute_bits)

How much space will be occupied if String were drawn in Fontable? Lbearing is the number of pixels to the left of the origin point; RBearing is the number of pixels to the right of the origin point; Ascent is the number of pixels above the origin point; and Descent is one greater than the number of pixels below the origin point. The reason Descent is one greater than what you would expect is that it allows you to add Ascent and Descent to determine the height of String.

String may be either an atom or list of character codes.

This differs from text_extents only in that it does not force ProXL to load the sizes of all the characters in the font from the server. If this information has already been loaded, query_text_extents will use it. It is usually better to use text_extents, since once the information is loaded from the server, it is much faster to determine the size of a string. So if you will ever want to find the size of another string in the same font, you should probably use text_extents.