Sentence:  In their very first collages , Braque and Picasso draw or paint over and on the affixed paper or cloth , so that certain of the principal features of their subjects as depicted seem to thrust out into real , bas-relief <WSD>space</WSD> - or to be about to do so - while the rest of the subject remains imbedded in , or flat upon , the surface . 
Meaning of the word marked with <WSD> tags:  an empty area (usually bounded in some way between things)