Enforce no spacing within parskip package

Question

I would like to apply parskip package for some paragraphs, but not other paragraphs within the document. Is there a way to do so?

Currently, if I use \usepackage[indent = 20pt]{parskip}, the setting applies to the whole document. Is there a way to disable this setting for some paragraphs in the document?

Answer 1

First scenario: some paragraphs should be spaced.

\documentclass{article}
\usepackage{lipsum}% for mock text
\newenvironment{spacedpars}{%
  \par
  \setlength{\parskip}{1ex plus 0.2ex minus 0.1ex}%
  \addvspace{\skipeval{\topsep-\parskip}}%
}{\par\addvspace{\topsep}}
\AtBeginDocument{%
  \setlength{\parindent}{20pt}% huge indentation! 
}
\begin{document}
\lipsum[1][1-4]\par
\lipsum[2][1-4]\par
\lipsum[3][1-4]
\begin{spacedpars}
\lipsum[4][1-3]\par
\lipsum[5][1-3]\par
\lipsum[6][1-3]
\end{spacedpars}
\lipsum[7][1-4]\par
\lipsum[8][1-4]\par
\lipsum[9][1-4]
\end{document}

Second scenario: some paragraphs should not be spaced.

\documentclass{article}
\usepackage[indent=20pt]{parskip}
\usepackage{lipsum}% for mock text
\newenvironment{unspacedpars}{%
  \par
  \setlength{\parskip}{0pt plus 0.1pt}
  \addvspace{\topsep}%
}{\par\addvspace{\topsep}}
\begin{document}
\lipsum[1][1-4]\par
\lipsum[2][1-4]\par
\lipsum[3][1-4]
\begin{unspacedpars}
\lipsum[4][1-3]\par
\lipsum[5][1-3]\par
\lipsum[6][1-3]
\end{unspacedpars}
\lipsum[7][1-4]\par
\lipsum[8][1-4]\par
\lipsum[9][1-4]
\end{document}