如何缩进 mdframed 环境的第一行？

Question

我被要求在用 定义的环境中缩进第一段mdframed。

我看过这个问题mdframed 环境中的段落缩进，虽然它提供了一种解决方法，但实际上必须有一种更巧妙的方法来做到这一点。（我在手册中找不到任何迹象表明提供了此功能；像这样的选项[indentfirst = true]真的很好。）

这是测试文件：

\documentclass[11pt]{amsbook}
\usepackage{tikz}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{etoolbox}

% define (using mdframed) a highlighted block with a double line on the
% left along the (inside) edge of the text block.
%
\mdfdefinestyle{twolined}{%
   leftline=true,rightline=false,topline=false,bottomline=false,%
   outerlinewidth=.7pt,innerlinewidth=.7pt,middlelinewidth=2pt,%
   outerlinecolor=black,innerlinecolor=black,middlelinecolor=white,%
   innerleftmargin=6pt,innerrightmargin=0pt,%
   innertopmargin=0pt,innerbottommargin=0pt,%
%   splittopskip=0pt,splitbottomskip=0pt.%
   skipabove=.5\baselineskip,skipbelow=.5\baselineskip
}
\newmdenv[%
   leftline=true,rightline=false,topline=false,bottomline=false,%
   outerlinewidth=.7pt,innerlinewidth=.7pt,middlelinewidth=2pt,%
   outerlinecolor=black,innerlinecolor=black,middlelinecolor=white,%
   innerleftmargin=6pt,innerrightmargin=0pt,%
   innertopmargin=0pt,innerbottommargin=0pt,%
%   splittopskip=0pt,splitbottomskip=0pt.%
%   skipabove=.5\baselineskip,skipbelow=.5\baselineskip%
   skipabove=1\baselineskip,skipbelow=.5\baselineskip%
]{linedintro}

% patch the command on which linedintro is based, to try to restore the
% paragraph indentation on the first line.
%
\makeatletter
\patchcmd\mdf@lrbox
   {\parindent\z@}{\parindent\normalparindent\relax}{}{}
\makeatother

\begin{document}
\thispagestyle{empty}

\noindent Some unindented random text.

\begin{linedintro}
First paragraph within the lined environment.
Add some text to make it two lines long.

Second paragraph within the lined environment.  Make it two lines long.
\end{linedintro}

\noindent Some more unindented random text.
\end{document}

输出：

我尝试重置其他实例\parindent，但没有效果。（我可能只是在错误的地方寻找，但不清楚是什么是正确的地方。

如果我将定义中的环境重命名为xlinedintro并添加“衍生”环境

\newenvironment{linedintro}{%
  \begin{xlinedintro}
  \parindent\normalparindent
  \hspace*{\normalparindent}\ignorespaces
 }{%
  \end{xlinedintro}%
}

这将强制在第一段缩进。但实际情况要复杂得多，有时marginnote在环境的开头和实际文本之间必须有其他东西（a），因此需要小心输入以避免出现多余的不必要的空间。

是有没有更好的地方应用补丁？或者有其他更巧妙的方法来实现缩进？

Answer 1

我可以为其提供一个补丁，linedintro以便依次进行修补\mdf@lrbox并\mdf@trivlist（本地）添加所需的缩进。

\documentclass[11pt]{amsbook}
\usepackage{tikz}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{etoolbox}

% define (using mdframed) a highlighted block with a double line on the
% left along the (inside) edge of the text block.
%
\mdfdefinestyle{twolined}{%
   leftline=true,rightline=false,topline=false,bottomline=false,%
   outerlinewidth=.7pt,innerlinewidth=.7pt,middlelinewidth=2pt,%
   outerlinecolor=black,innerlinecolor=black,middlelinecolor=white,%
   innerleftmargin=6pt,innerrightmargin=0pt,%
   innertopmargin=0pt,innerbottommargin=0pt,%
%   splittopskip=0pt,splitbottomskip=0pt.%
   skipabove=.5\baselineskip,skipbelow=.5\baselineskip
}
\newmdenv[%
   leftline=true,rightline=false,topline=false,bottomline=false,%
   outerlinewidth=.7pt,innerlinewidth=.7pt,middlelinewidth=2pt,%
   outerlinecolor=black,innerlinecolor=black,middlelinecolor=white,%
   innerleftmargin=6pt,innerrightmargin=0pt,%
   innertopmargin=0pt,innerbottommargin=0pt,%
%   splittopskip=0pt,splitbottomskip=0pt.%
%   skipabove=.5\baselineskip,skipbelow=.5\baselineskip%
   skipabove=1\baselineskip,skipbelow=.5\baselineskip%
]{linedintro}

% patch the command on which linedintro is based, to try to restore the
% paragraph indentation on the first line.
%
\makeatletter
\newcommand{\indentforlinedintro}{%
  \patchcmd\mdf@lrbox{\parindent\z@}{\parindent\normalparindent\relax}{}{}%
  \patchcmd\mdf@trivlist{\itemindent\z@}{\itemindent\normalparindent}{}{}%
}
\patchcmd{\linedintro}{\begin}{\indentforlinedintro\begin}{}{}
\makeatother

\begin{document}
\thispagestyle{empty}

Some random text.
Some random text.
Some random text.
Some random text.
Some random text.
Some random text.
Some random text.
Some random text.

\begin{linedintro}
First paragraph within the lined environment.
Add some text to make it two lines long.

Second paragraph within the lined environment.  Make it two lines long.
\end{linedintro}

\noindent Some more unindented random text.
\end{document}

钥匙indent=也许确实非常有用。