我对以下代码有疑问：
\newtoks\sectoks
\sectoks={\noindent}
\newtoks\subsubjectstyle
\subsubjectstyle={\emitsectglue 1\the\sectoks}
\newtoks\postsectoks
\postsectoks={\par\smallskip\noindent\kern-1sp\hskip1sp}
\long\def\subsubject#1\par{%
{\the\subsubjectstyle#1}\the\postsectoks}
\def\emitsectglue#1{%
\ifdim\lastskip=1sp
\nobreak
\else
\vskip0pt plus#1\baselineskip
\penalty-\numexpr#1*100+50\relax
\vskip0pt plus-#1\baselineskip
\vskip#1\baselineskip
\fi}
\long\def\blockquote#1\eol{%
\emitsectglue 1
\begingroup
\raggedright\narrower\noindent #1
\smallskip
\endgroup\noindent}
\tracingall
\subsubject
The following subsubject will choose the first if's true-branch.
\subsubject
But the following blockquote will not. Why is that?
\blockquote
Be conservative in what you send, liberal in what you receive
\eol
\bye
当使用该\subsubject命令后跟另一个命令时\subsubject，宏将按预期工作并且不会添加垂直粘贴和负惩罚。
但是，当使用另一个命令使用完全相同的代码时，突然\if没有选择正确的分支。我不明白为什么会这样。
答案1
\relax在之后添加\hskip1sp：TeX 在寻找跳过规范时会扩展标记，并且在\blockquote跟随时，规范尚未完成，因此扩展会\ifdim在插入跳过之前进行评估。
如果\subsubject如下，则没有问题，因为替换文本中的第一个标记是{停止扩展的标记。
我会支持这一论点，\emitsecglue并消除几个可能的虚假空间源：
\newtoks\sectoks
\sectoks={\noindent}
\newtoks\subsubjectstyle
\subsubjectstyle={\emitsectglue{1}\the\sectoks}
\newtoks\postsectoks
\postsectoks={\par\smallskip\noindent\kern-1sp\hskip1sp\relax}
\def\subsubject#1\par{%
{\the\subsubjectstyle#1}\the\postsectoks}
\def\emitsectglue#1{%
\ifdim\lastskip=1sp
\nobreak
\else
\vskip0pt plus#1\baselineskip
\penalty-\numexpr#1*100+50\relax
\vskip0pt plus-#1\baselineskip
\vskip#1\baselineskip
\fi}
\long\def\blockquote#1\eol{%
\emitsectglue{1}%
\begingroup
\raggedright\narrower\noindent #1%
\smallskip
\endgroup\noindent}
\subsubject
The following subsubject will choose the first if's true-branch.
\subsubject
But the following blockquote will not. Why is that?
\blockquote
Be conservative in what you send, liberal in what you receive
\eol
\bye