Just wanted to add - child that I am of the throw-away second half of the twentieth century, I throw holey socks away rather than take a needle and cotton to them. But if I did take a needle and cotton to them, I'd be darning them rather than mending them.(PS. Although I know the word "darn", I'll be darned if I ever heard it. It is usually "mend").
Oh gosh, Lis, I remember doing that nail-varnish thing! (But I wouldn't actually have called it mending - not sure what I'd have called it, other than "sticking nail varnish on it"....). In the Beatles song, I'm sure "mending" was chosen because it rhymed with "never ending".Actually in the era when the Beatles were singing that song, most of the girls I knew, including myself, used to darn our stockings with needle and thread. If we just mended them, it would mean we dabbed some nail varnish on the run to stop it progressing.
That does not mean you did it while running, does it?we dabbed some nail varnish on the run