Sentence:  One seldom hears a text sung in which 50 per cent of the lines are not mere <WSD>fill-outs</WSD> — either, on the mechanical level, excuses for rhymes or scansion or, on a more justifiable level, additions of emotional weight by mere reiteration of intellectual points already made. 
Meaning of the word marked with <WSD> tags:  Something extra that is added to increase the size of something.