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PDF 字符串中不允许使用标记，这是由带有可选参数的宏引起的吗？

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PDF 字符串中不允许使用标记，这是由带有可选参数的宏引起的吗？

带有可选参数的宏似乎会将 PDF 字符串中不允许的标记注入到输出中。

下面的 MWE 应该能证明这种效果。

这个令牌到底来自哪里，它是什么样子的，我做错了什么，有没有已知的解决方法？

\documentclass[12pt]{article}

\usepackage[main=english]{babel}

\newcommand{\docTitle}{Works fine}
\renewcommand{\docTitle}[1]{Works fine, too (#1)}
%\renewcommand{\docTitle}[1][]{Does not work}%<- simplified/minimized example

\usepackage[pdfencoding=auto,
final=true,
]{hyperref}
%\usepackage{hyperxmp}
\hypersetup{%
pdfauthor   = {John Doe},
pdftitle    = {\docTitle{Hiho!}},
pdfsubject  = {The Subtitle},
pdfkeywords = {Some keywords},
pdfdisplaydoctitle = true,
pdfstartpage = 1,
pdfstartview = FitH,
}

\setlength{\parindent}{0pt}

\begin{document}
Local tex-environment:

TexLive 2016 (latest updates, frozen), Win7-64bit, Texstudio (latest 
stable release)

\bigskip

Step to reproduce:

After uncomenting line~7 the content of \textbackslash docTitle is 
ignored (see screenshot of the resulting pdf's metadata).

\bigskip

The log says:

\begin{verbatim}
Package hyperref Warning: Token not allowed in a PDF string (PDFDocEncoding):
(hyperref)                removing `\docTitle' on input line 21.
\end{verbatim}

\bigskip

Question[s]:

Where does this token exactly come from, how does it look like, is there 
a known workaround?

\end{document}}

截屏：

在此处输入图片描述

答案1

由于宏具有可选参数，因此它不可扩展，因此PDF 元键中留下了\docTitle[]{}“无用”的标记。\docTitle

一个可能的解决方案：使用\DeclareExpandableDocumentCommand来自的宏xparse。

\DeclareExpandableDocumentCommand{\docTitle}{O{}m}{Does not work or does it? See #1}

将定义一个可扩展的宏O，该宏具有一个可选参数，没有默认值，因此只需使用即可{}将其留空。这xparse相当于\newcommand{\foo}[1][]{}。

\DeclareExpandableDocumentCommand定义的宏必须具有强制参数。

\documentclass[12pt]{article}

\usepackage[main=english]{babel}

\usepackage{xparse}
\newcommand{\docTitle}{Works fine}
\renewcommand{\docTitle}[1]{Works fine, too (#1)}
\DeclareExpandableDocumentCommand{\docTitle}{O{}}{Does not work or does it? See #1}%<- simplified/minimized example



\usepackage[pdfencoding=auto,
final=true,
]{hyperref}

%\usepackage{hyperxmp}
\hypersetup{%
  pdfauthor={John Doe},
  pdftitle={\docTitle[FooFoo]{Hiho}},
  pdfsubject  = {The Subtitle},
  pdfkeywords = {Some keywords},
  pdfdisplaydoctitle = true,
  pdfstartpage = 1,
  pdfstartview = FitH,
}

\setlength{\parindent}{0pt}

\begin{document}
Local tex-environment:

TexLive 2016 (latest updates, frozen), Win7-64bit, Texstudio (latest 
stable release)

\bigskip

Step to reproduce:

After uncomenting line~7 the content of \textbackslash docTitle is 
ignored (see screenshot of the resulting pdf's metadata).

\bigskip

The log says:


\bigskip

Question[s]:

Where does this token exactly come from, how does it look like, is there 
a known workaround?

\end{document}}

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