Short interline spacing after \item in customized description environment

Question

I'm working on a technical guide, and I have a list of descriptions of different commands that can be run. Some of these commands have aliases or alternative invocations, and I want them to have the same description body. Using the enumitem package, I've managed to customize this to look the way I want. What I have looks like the following:

\documentclass{book}

\usepackage{lipsum}
\usepackage{enumitem}

\SetLabelAlign{parleft}{\parbox[t]\textwidth{#1}}

\begin{document}

\begin{description}[style=nextline,labelindent=0em,align=parleft]
\item[There's just one phrase, notice hanging characters]
    Here Is The Definition Of The Phrase. \lipsum[11]
\item[This is the first phrase \newline Notice hanging characters in the second phrase]
    Here Is The Definition Of The Phrase. \lipsum[47]
\end{description}

\end{document}

Items that just have a single line look perfectly fine to me, but when there are multiple lines, the spacing between the last line in the \item and the following description is much shorter than the spacing between the lines inside the item and between single-line items and their descriptions:

I have two questions:

• To help my understanding of TeX, why is the space after the \parbox that contains a single line correct, but the space after the one with two lines is not?
• How can I fix this so that the space after the last line in every \item to the description is equivalent?

Note that this document is auto-generated, so a solution that doesn't require manual intervention for each multi-line item is preferred, but I can customize the generation as needed.

Thanks in advance!

Answer 1

This might be a way of achieving what you want:

\documentclass{book}
\usepackage{lipsum}
\usepackage{enumitem}
\SetLabelAlign{parleft}{\parbox[t]\textwidth{#1\smallskip}}
\begin{document}
\begin{description}[style=nextline,labelindent=0em,align=parleft]
  \item[There's just one phrase, notice hanging characters]
  Here Is The Definition Of The Phrase. \lipsum[11]
  \item[This is the first phrase  \newline Notice hanging characters in the second phrase]
  Here Is The Definition Of The Phrase. \lipsum[47]
\end{description}
\end{document}

Answer 2

Adding a \vskip\partopsep seem to work:

\documentclass{book}

\usepackage{lipsum}
\usepackage{enumitem}

\SetLabelAlign{parleft}{\parbox[t]\textwidth{#1\vskip\partopsep}}

\begin{document}

\begin{description}[style=unboxed,labelindent=0em,align=parleft]
\item[There's just one phrase, notice hanging characters]
    Here Is The Definition Of The Phrase. \lipsum[11]
\item[This is the first phrase \newline Notice hanging characters in the second phrase]
    Here Is The Definition Of The Phrase. \lipsum[47]
\end{description}

\end{document}