我想在兩個部分標題之間添加一個額外的垂直空間（如果它們相互跟隨），即它們之間沒有其他文字或其他任何內容。是否有一些條件 if 指令可能使用 if@aftersection... 之類的東西？
\documentclass[12pt, a4paper]{memoir}
\usepackage[utf8]{inputenc}
\begin{document}
\chapter{Chapter title}
\section{A first section title}
\section{A second section title}
Just some text. There should be a conditional vspace between the first
section and the second section if there is nothing else between them.
\section{A third section}
Some more text here.
\section{A fourth section}
Some more text.
\end{document}
答案1
一般來說，您必須適應以下提供的所有可能的參數組合memoir的\section.具體來說，它需要兩個可選參數（對於目錄和運行標頭）。除此之外，還可以掃描以查看下一個令牌是否正在\section使用\@ifnextchar：
\documentclass{memoir}
\usepackage{xparse}
\let\oldsection\section
\makeatletter
\RenewDocumentCommand{\section}{s o o m}{%
\IfBooleanTF{#1}
{\oldsection*{#4}}
{\IfValueTF{#2}
{\IfValueTF{#3}
{\oldsection[#2][#3]{#4}}
{\oldsection[#2]{#4}}}
{\oldsection{#4}}}%
\@ifnextchar\section{\vspace{5\baselineskip}}{}%
}
\makeatother
\begin{document}
\tableofcontents
\chapter{Chapter title}
\section{A first section title}
\section{A second section title}
Just some text. There should be a conditional \verb|\vspace| between the first
section and the second section if there is nothing else between them.
\section{A third section}
Some more text here.
\section{A fourth section}
Some more text.
\end{document}
這是另一個選擇：
定義一個取得三個參數的巨集\ifnextcommandis{<this>}{<true>}{<next>}。您指定<this>和<true>，並且假定巨集後面的任何內容都將是<next>巨集：
\newcommand{\ifnextcommandis}[3]{%
\def\thiscommand{#1}% Store this command
\def\nextcommand{#3}% Store next command
\ifx\nextcommand\thiscommand\relax
#2%
\fi
\nextcommand}% Re-insert next command
\let\oldsection\section
\RenewDocumentCommand{\section}{s o o m}{%
\IfBooleanTF{#1}
{\oldsection*{#4}}
{\IfValueTF{#2}
{\IfValueTF{#3}
{\oldsection[#2][#3]{#4}}
{\oldsection[#2]{#4}}}
{\oldsection{#4}}}%
\ifnextcommandis{\section}{\vspace{5\baselineskip}}%
}