How do I set \itemsep to rubber length?

Question

I know that I can set \itemsep to any length like this,

\setlength{\itemsep}{0pt}

But if I want to set \itemsep to a rubber length (e.g. \bigskip), how do I do this?

\setlength{\itemsep}{\bigskip} 

does not work.

Answer 1

The skip is \bigskipamount; \bigskip is a \vskip of \bigskipamount, so you could use

 \setlength{\itemsep}{\bigskipamount}

Of course, you can say

 \setlength{\itemsep}{12pt plus4pt minus4pt}

For the record, the definitions in Plain:

\newskip\smallskipamount % the amount of a \smallskip
\smallskipamount=3pt plus1pt minus1pt
\newskip\medskipamount % the amount of a \medskip
\medskipamount=6pt plus2pt minus2pt
\newskip\bigskipamount % the amount of a \bigskip
\bigskipamount=12pt plus4pt minus4pt

\def\smallskip{\vskip\smallskipamount}
\def\medskip{\vskip\medskipamount}
\def\bigskip{\vskip\bigskipamount}

and in the LaTeX kernel:

\def\smallskip{\vspace\smallskipamount}
\def\medskip{\vspace\medskipamount}
\def\bigskip{\vspace\bigskipamount}

\newskip\smallskipamount 
\smallskipamount=3pt plus 1pt minus 1pt
\newskip\medskipamount
\medskipamount =6pt plus 2pt minus 2pt
\newskip\bigskipamount
\bigskipamount =12pt plus 4pt minus 4pt