Thank you, but you can do it with this command
{=proper({clipboard})}
Actually, you gave me an idea of how to do it with a little bit of extra code:
{words=split({clipboard}, " ")}{repeat: for word in words}{if: contains("and, or, but, nor, yet, so, for, a, an, the, in, to, of, at, by, up, for, off, on",{=lower(word)})}{=lower(word)}{else}{=proper(word)}{endif} {endrepeat}
So, thank you for the hint!