{tex-core} is for questions that are independent of formats and macro packages. Such questions usually relate to low-level TeX programming or the behaviour of TeX at an underlying level. Note that even Plain TeX is a format in itself; for questions about it, use {plain-tex}.

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17
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3answers
3k views

\string command behavior - Plain TeX

I would like to learn Plain TeX and I'm reading Knuth's "The TeXBook". At Chapter 7, Knuth talks about the \string command and how it converts control sequences into lists of characters tokens. Why ...
17
votes
4answers
2k views

How to make a real backslash (escape) character?

I just want a good way to make a backslash character (or whatever character(s) any given format uses as escape characters), suitable to \write to a file or pass to a pdfTeX primitive. Let me ...
17
votes
2answers
380 views

Why does this simple \ifx test fail?

This should be easy, but I don't understand why the test below fails... I expected Hurrah! to be printed when the \currentchar count reaches 90 (i.e. the character code of Z). There must be some ...
17
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2answers
2k views

When is it good practice to use \unskip

One sees in source2e the command \unskip used in various places. My understanding in general terms is that the macro is the equivalent of \ignorespacesbehind. Where would it be recommended to use ...
17
votes
2answers
359 views

Use of \everyeof and \endlinechar with \scantokens

The e-TeX \scantokens primitive allows retokenization of input. However, it is almost always used in a group where \everyeof and \endlinechar are set (see for example Can I convert a string to catcode ...
17
votes
2answers
331 views

When is \relax necessary after a \ifcase#1 statement

In the LaTeX kernel (latex.ltx) we see some examples of \ifcase#1\or a\or b\or ... (an \ifcase without an added \relax), but when we look at some packages most of them add this statement after the ...
17
votes
3answers
226 views

Is it possible to interact with TeX mid-process?

Quoting from an answer to Typesetting the entire Song That Never Ends I ran this code once, and aborted the process after it reported producing something like 47,000 pages (in a very short amount ...
17
votes
4answers
695 views

Detokenizing without extra spaces?

I have a need to pass through potentially arbitrary characters untouched and found this macro: \def\test#1{\expandafter\zap@space\detokenize{#1} \@empty} The problem is that \detokenize inserts ...
17
votes
1answer
810 views

How does TeX handle \else and \fi in conditionals?

I have seen packages using \def\afterelse#1\else#2\fi{\fi#1} which TeX seems happy to accept. But on taking the first branch, isn't TeX expecting \else instead of \fi? That is, isn't the following ...
17
votes
1answer
288 views

Why are \new… defined as \outer in the plain TeX format?

In plain.tex, D.E.Knuth decided to define as \outer all the macros which allocate registers: \newcount, \newdimen, \newskip, \newread, \newwrite. This forbids them from entering the argument of ...
17
votes
3answers
314 views

Can I convert a string to catcode 11?

In the TeX FAQ there's a way to test if the jobname is equal to something (comparing the jobname). The difficulty of the naïve test is that the contents of the \jobname primitive are catcode 12 so to ...
17
votes
1answer
141 views

What primitives can expandably tell us about the current horizontal list?

I've been writing some code that expands macros and catches characters and non-expandable primitives as they reach TeX's stomach, and I encountered an issue: since I gather letters one by one, with ...
16
votes
3answers
2k views

Defining commands that are scoped to a particular environment

Is it possible to define commands in a separate namespace so that they only work within a particular environment? For example, can I create a package named foo that defines a foo environment and a ...
16
votes
2answers
639 views

How does one publish/promote a new package?

I just took all the wonderful information supplied here, and wrote a small package that makes it possible to use Unicode characters for section, subsection, subsubsection, paragraph, subparagraph and ...
16
votes
2answers
386 views

Filling gaps by repeating a character

I want to create a macro like \mymacro that has four arguments; first and fourth arguments are any letters, second argument is a character and the third argument is a length. When I say \mymacro{م} ...
16
votes
3answers
952 views

Does `\noexpand` have to be a primitive?

Background: I'm trying to deepen my understanding of TeX and how the intricacies work (spurred a little by this place, I should say, and hoping one day to not be a "Cargo Cult Programmer" - see When ...
16
votes
1answer
988 views

What does \marks do?

Recently I had cause to define a macro called \marks. If I try something like \newcommand{\marks}{fred} I get the error ! LaTeX Error: Command \marks already defined. In LaTeX, if I do ...
16
votes
4answers
771 views

Selectively suppress generation of typeset output

Is it possible put TeX into a "mute" mode in which all typesetting is suppressed? \documentclass{article} \pagestyle{empty} \begin{document} \suppress This text will not be seen in the generated ...
16
votes
1answer
288 views

Ligatures and hyphenations: the effect of empty brace groups {}

For the following example, \hsize =2in shelf{}ful shelf{}ful shelf{}ful rot{}ten rot{}ten shelf{}ful shelf{}ful shelf{}ful shelf{}ful shelf{}ful rot{}ten rot{}ten shelf{}ful shelf{}ful \bye The ...
16
votes
1answer
960 views

How do \lastskip and \ifdim work?

I thought I knew the answer to this question, but I can't understand the following plain TeX code: \noindent\hskip1pt\ifdim\lastskip=0pt lastskip was 0pt\fi\par \noindent\hskip1pt\showthe\lastskip ...
16
votes
1answer
525 views

Is \toks necessary to define \g@addto@macro? Can token registers be avoided in generel?

In LaTeX2e kernel, there is a useful macro \g@addto@macro: \long\def\g@addto@macro#1#2{% \begingroup \toks@\expandafter{#1#2}% \xdef#1{\the\toks@}% \endgroup} However, I think the ...
16
votes
1answer
833 views

\jobname, character codes and \detokenize

I recently wanted to compare \jobname to a string (with the xstring package) and was rather surprised that the string never matched. Tho internet told me that I had to use \detokenize on the string. ...
16
votes
1answer
315 views

Semantics of negative glues

This question is about the semantics of glues like 0pt plus -1fill, where the coefficient in front of the fill is negative. The following minimal example shows my attempt to figure this out ...
15
votes
4answers
851 views

\aftergroup a list of tokens

\aftergroup executes the next token after the end of the current group. Is there a variant, \Vaftergroup{\some\tokens\a\b} that would put \some\tokens\a\b after the current group ends? Of course, one ...
15
votes
4answers
774 views

File copy without expansion

What is the command for file copy? I want to copy the contents of one file into another without any command expansion. In a command line driven operating system one would use copy source target I ...
15
votes
2answers
179 views

Multiple consecutive \par's equivalent to just one?

I think the answer to this question should be positive but I just couldn't find it answered elsewhere: Are multiple consecutive \par's the same as a single \par? For example, is \par\par the same as ...
15
votes
3answers
341 views

Parsing strings containing diacritical marks (macros?)

I apologize that this question may seem very much like several other recent ones I have asked (Parsing leading hardspaces, Parsing a \$ as part of an improved \getargs command). They are all related ...
15
votes
4answers
554 views

LaTeX, package documentation look-up

I am on OS X (10.6 Snow Leopard) using TeXLive-2011 to typeset a simple .tex file I am editing in Vim and trying to learn. My problem is: how do I... gradually learn about what TeX can do for me get ...
15
votes
3answers
2k views

Difference between \mskip and \mkern

What are the differences between \mskip and \mkern? The TeXbook writes the following (ch. 18): You can insert math glue into any formula just by giving the command ‘\mskip⟨muglue⟩’. [...] ...
15
votes
2answers
193 views

\expandafter with \uppercase ordering

As I understand it, the behavior of \expandafter is such that if \a and \b are macros, then \expandafter\a\b will first expand \b then \a. But my understanding must be wrong, because I don't ...
15
votes
4answers
341 views

Using the filename in the document?

I have a bunch of documents called wk01.tex wk02.tex and so on up to (eventually) 20. These are weekly handouts for a course I TA. Currently, each document starts with a \def\classweek{5} or whatever. ...
15
votes
2answers
472 views

Why does `x_\text y` work?

As far as I have understand the tokenization in LaTeX, x_\text y will be split up into x _ \text y Now the _ will consume/bind to the next token. However, \text takes an argument as well. If _ ...
15
votes
2answers
1k views

How to add a hook to a macro

LaTeX uses hooks extensively, one method employed is the command g@addto@macro. It is defined in source2e as: \long\def\g@addto@macro#1#2{% \begingroup \toks@\expandafter{#1#2}% ...
15
votes
2answers
715 views

What is the difference between square brackets and curly brackets in a command invocation?

Pardon the naive beginner question. In a command like: \textcolor[HTML]{4C7045}{dark green text}, or \documentclass[12pt]{article}, or \begin{figure}[htb], why are some arguments surrounded by [] and ...
15
votes
2answers
4k views

Difference between setting parindent and hangindent

Is there a difference between setting \parindent to 1em and to setting \parindent to 0em, \hangindent to 1em, and \hangafter to -1 that shows in practical use? The nodes created by TeX are ...
15
votes
3answers
819 views

\def taking rest of the line as argument

I know how to define a macro that will take the rest of the paragraph as parameter. Simply write \def\a#1\par{\textbf{#1}}. But, how do I write a macro whose argument will extend to the end of the ...
15
votes
1answer
222 views

\def two macros with same name, but different argument syntax

Is it possible to have macros with the same name, but different “syntax”? E.g. we have the primitive \font which could be seen as having 3 arguments(a. without size information; b. giving the ...
15
votes
3answers
615 views

Unbalanced output routine

The TeX primitive \output behaves almost like a toks register, except in the fact that it is always surrounded by braces. For instance, after \output={\plainoutput}, the result of \showthe\output is ...
15
votes
2answers
200 views

Test whether \end will really end the run

Can I test whether calling the \end primitive will really end the run? The naive \ifdim\pagegoal=16383.99998pt yes\else no\fi is not sufficient (even adding to that mix \deadcycles). According to ...
15
votes
1answer
319 views

How can latex and pdflatex be both symbolic links to same executable (pdftex) and not behave the same?

When I run $ latex my_doc.tex and $ pdflatex my_doc.tex it works, and when I run $ pdftex my_doc.tex it doesn't work. The thing is I noticed that both LaTeX and pdflatex commands are ...
15
votes
1answer
481 views

How do I ‘expand’ a control sequence `\let` to a character?

Consider the following: \let\1=X \edef\2{\1} \show\1 \show\2 The result is > \1=the letter X. > \2=macro: ->\1. Is it possible to ‘expand’ the meaning of \1 so that \2 contains just ...
15
votes
0answers
179 views

Test if paragraph has an overfull line

I'd like to test if the last paragraph has any overfull line. The naive approach of looking at the \badness once the paragraph is finished does not work, as it will only give the badness of the last ...
14
votes
7answers
2k views

Can I see a plain TeX source file please?

all the LaTeX-tutorials tell me how LaTeX is an extention simplifying the building of TeX documents. Understandably, no one uses plain TeX anymore, right? But I seem to learn better when I grasp the ...
14
votes
3answers
3k views

What is the difference between \empty and \@empty?

I want to elaborate a command that would print differently simple differential dx and multidimensional differential d^3x. For this purpose I invented the command \dif with one optional argument. It is ...
14
votes
2answers
502 views

Why using character ^^ff before every chapter in the TeXBook source

When viewing the source code of the TeXBook, I find that there is a character ^^ff before every chapter in it. I am wondering why using this ^^ff character which seems useless? The following ...
14
votes
3answers
784 views

TeX macro and command expansion?

I have implemented couple of macros that should remove commas from numbers. It's nasty dirty stuff, but it works when input is number: \removecommas{12,34,56.7} % => 123456.7 But it stop working ...
14
votes
3answers
655 views

Is there a printable version of a reference manual for all TeX primitives?

Everywhere in the TeX community, I see suggestions like \parskip, \obeylines, \parindent, etc. I'd be surprised not to find them even in the most basic LaTeX packages. So I figured they must be deeper ...
14
votes
2answers
220 views

How can own commands be aware of \global?

When I define a command that defines commands \def\makefoobar{ \def\foo{foo} \def\bar{bar} } and prefix it with \global { \global\makefoobar } it is treated like { \global\def\foo{foo} ...
14
votes
2answers
892 views

Is a TeX macro defined?

I am looking for a way in TeX to check if a macro was defined. Currently I use a rather tangled way. I exploit a sort of side effect when comparing two macros via \ifx; this command returns: true, ...
14
votes
2answers
3k views

\llap (or \rlap) at the begining of an indented paragraph

If I use a \llap{text} command at the begining of an indented paragraph, the text is not indented and is put on the line above the paragraph. \documentclass{article} \begin{document} \parindent=2cm ...