SWI-Prolog -- Instance variables

label <- font: font: Font used to display the label. Note that the font is only applicable if the label<-selection’s value is a char_array object (text).
label <- length: 0..: Width of the label's field in ex units (i.e. width of the character x in the current label<-font).
label <- selection: char_array|image: Currently displayed text or image object. If the selection is a text (instance of class char_array), it is displayed in label<-font. If it is a markup object, the markup is rendered, mixing fonts, styles and (theme) colours. The label<-font is used for text without a font in the markup. If the label is not active, the colours of the text in the markup are ignored. The field width is described by label<-length. If the actual text does not fit in the field the label is automatically enlarged.