I am trying to edit the style svmono.cls to tweak the default spacings, but there are entries whose values are not clear to me. In particular, what are \z@ and \p@ in the definitions in lines 244 and 587 (see below)? Thanks, Jorge.
EXCERPT FROM svmono.cls:
\setlength{\parskip}{\z@ \@plus \p@}
\renewcommand\section{\@startsection{section}{1}{\z@}%
{-30\p@}% \p@lus -4\p@ \@minus -4\p@}%
{16\p@}% \p@lus 4\p@ \@minus 4\p@}%
{\normalfont\secsize\secstyle
\rightskip=\z@ \@plus 8em\pretolerance=10000 }}
\z@is0ptand\p@is1pt, so-4\p@is4pt. – egreg Apr 26 '18 at 21:490pt plus 1ptis not0ptit is a stretchy (rubber) length with natural width 0pt and allowed to stretch to 1pt. – David Carlisle Apr 26 '18 at 22:03