{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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12
votes
2answers
1k views

Breakable vboxes

In Plain TeX how can I make vboxes breakable, and can I handle/measure them separately? What I'm trying to do, is that I have a portion of text, that is treated separately (no indention, narrower, ...
12
votes
2answers
271 views

Define a shortcut (-> to \rightarrow) in plain TeX

I'ld like to make -> a shortcut for \rightarrow. Is that possible with Plain TeX or has it to do with the loaded font?
12
votes
2answers
419 views

How is \unexpanded defined?

I was wondering how \etoolbox's \expandonce does what it does. So I looked up how it was defined and found \unexpanded\expandafter{#1} But no matter where I look, I cannot find a definition for ...
12
votes
2answers
182 views

What would be a suitable replacement for ifcsname in a non-etex situation?

From the pgfkeys.code.tex file: % This is useful: \def\pgfkeys@ifcsname#1\endcsname#2\else#3\fi{\expandafter\ifx\csname#1\endcsnam e\relax#3\else#2\fi}% \ifx\eTeXrevision\undefined% \else% ...
12
votes
2answers
265 views

How are dashes implemented in TeX?

How does LaTeX implement the differences between the dashes? -, --, and --- all print different dashes, but - is not an active character: it has catcode 12, the same as digits like 2.
12
votes
5answers
2k views

Teach me how to use \loop…\repeat constructs, etc

The following code snippet is a part of the solution given here: \def\IncludeOutput#1{ \parskip=2mm \def\examplename{#1} \pdfximage{\Directory/\examplename.pdf}% ...
12
votes
5answers
756 views

Test if token is a control sequence

Sometimes more complex (La)TeX macros test the next input token and branch dependent on its type. I'm aware how to test for catcodes and character codes, but sometimes I like to handle control ...
12
votes
2answers
576 views

All about \shipout

While reading about packages that allow to hook macros to certain events, I came across this command, \shipout. Searching on the internet didn't help a lot but if I'm not so wrong it's somehow related ...
12
votes
1answer
566 views

What does \empty do? [duplicate]

What does it do and what are its applications? I am currently testing the subtitle of my beamer presentation for its string length to decide about line spacings. Could it be simpler using \empty? If ...
12
votes
2answers
152 views

Document equivalence

What is the best way to determine, for two arbitrary input files, if they will result in the same compiled document (disregarding timestamp information and external files)? Context I'm attempting to ...
12
votes
2answers
196 views

Can I detect whether a footnote has been split?

Title sez it all: Can I detect, hopefully by inspecting \box\footins, whether a footnote has been split at page-breaking? I found the package fnbreak but it uses labels, which is much too delayed for ...
12
votes
1answer
836 views

From LaTeX with pdflatex to plain TeX

I've always wanted to try plain TeX instead of LaTeX. I can use plain but I'm not able to use correctly the fonts and I'm not able to use the french hyphenation. I would to know how to do this with ...
12
votes
2answers
796 views

Tricks to make macros expandable

Expandable macros are useful (I find working in the lion's mouth super cool). But they are difficult to write. Can more experienced users give hints that help achieve expandability? For example, we ...
12
votes
1answer
189 views

How to get the natural width of the last box in a paragraph?

I want to get the natural width of the last line in a paragraph. For example, the last line of the following paragraph Georg Friedrich Bernhard Riemann (September 17, 1826 – July 20, 1866) was an ...
12
votes
1answer
201 views

Array functionality in TeX?

I've been using LaTeX for a while, but only recently I made myself a mission to create a class. I needed to learn the details of TeX, and I couldn't find answers to some of my questions. One of them ...
12
votes
1answer
1k views

Why does \hss fail?

Please why does the following fail? % \hss -> \hskip 0pt plus 1fil minus 1fil \setbox0=\hbox{a}% \setbox0\hbox to 10mm{\hss\unhbox0\hss} \unhbox0 And what makes LaTeX's ...
12
votes
2answers
445 views

New lines and TeX: difference between ^^J and ^^M

What is a new line for TeX in the following contexts: When reading from a file. When writing to a file. After having read a % character. In a \scantokens. I am asking in particular because the ...
12
votes
1answer
880 views

What is the function of \noalign?

The use of \noalign is quite common. For example here \noalign is used with \vskip{}to control the height of a table cell. How does \noalign work in general, and how does it work with \vskip? ...
12
votes
1answer
783 views

How to prevent extra spaces between two specific words when justification occurs?

My document contains many short, justified lines, so the lines often appear with many spaces between words, e.g.: These words have a space so that they can fit nicely into the available ...
12
votes
1answer
275 views

\show with fewer lines?

I am writing some macros for general debugging purposes (See Yiannis' question). I am basically expanding a given input step by step, and printing the result to the terminal and log. In order for this ...
12
votes
1answer
96 views

Tight connection of \vbox es

I don't understand why TeX put a thin whitespace between my two vertical boxes: \documentclass{article} \begin{document} \vbox to 1cm {\rule{1cm}{1cm}} \vbox to 1cm {\rule{1cm}{1cm}} ...
12
votes
1answer
170 views

Hide ^^^^-notation from pdftex

The following example gives when compiled with pdflatex the error ! Text line contains an invalid character. \documentclass{article} \usepackage{ifluatex} \ifluatex \usepackage{fontspec} \fi ...
12
votes
1answer
291 views

Test if a number is in a comma separated range/list of numbers

Martin Scharrer posted a very elegant answer for the question "Creating a zebra effect using listings". I want to extend that code to highlight only lines given in a comma separated list. The ...
12
votes
1answer
143 views

Inserting tokens at end of math mode

One can use \everymath and \everydisplay to insert tokens at the beginning of math mode, but what about inserting tokens at end of math mode? Lets say I want to enclose the math mode material in a ...
12
votes
1answer
872 views

Simple un-obfuscation of some LaTeX internals

Here's an example of some code from LaTeX's \DeclareFontFamily: \def\reserved@a{#3} \global \expandafter\let\csname #1+#2\expandafter\endcsname \ifx \reserved@a\@empty \@empty ...
12
votes
2answers
217 views

Assertions in Latex

I am writing a long latex document and use many macros for defining mathematical symbols. I would like to ensure that there is no clash in the notation. For example, something like ...
12
votes
1answer
336 views

Is Knuth's *The TeXBook* complete?

Suppose I want to learn TeX. Then, is The TeXBook a complete source? Does it cover all relevant aspect of TeX? Or is there something worth learning about TeX which is not present there? Does also ...
11
votes
2answers
553 views

() or {} after a command

I was wondering why for some commands it is "(...)" that follows, while for other commands it is "{...}". For example, "\exp(x)" and "\bar{x}". Are both () and {} for specifying the arguments for the ...
11
votes
3answers
494 views

Does the \relax side-effect of \csname…\endcsname still have a use?

I find it annoying that using \csname...\endcsname will define ... to be \relax if ... is undefined, and there is no improved primitive that does not have this side-effect, though there are partial ...
11
votes
4answers
217 views

Partially expanding a command

My \john command is defined like so: \def\john{\DontExpandMe} I would now like to repeatedly change its definition, to keep adding some extra stuff on the front. \foreach\i in {ape,bat,cow,dog} { ...
11
votes
3answers
426 views

Understanding etoolbox \ifdefempty and \ifdefvoid

I am trying to understand the etoolbox \ifdefempty and \ifdefvoid macros. The documentation says that \ifdefempty Expands to true if the control sequence is defined and is a parameterless macro ...
11
votes
3answers
428 views

Parser for decimal numbers in (plain) TeX

I need help writing a parser for decimal numbers using only TeX and plain TeX. The set of accepted inputs is given by the regular expression: (+-)?(0-9)*(.,)?(0-9)+ The parser need not do anything ...
11
votes
2answers
144 views

Does a space belong after pt?

Does a space always belong after pt, e.g. as used in \hskip1pt? If a space is used, are there situations where a space will appear where it is not intended? If no space is used, will pt be ...
11
votes
2answers
211 views

Creating new primitives

Consider the following TeX: \tt ~~~[def]: \meaning\def \par ~~~[let]: \meaning\let \par [define]: \meaning\define \par ~[macro]: \meaning\macro \def\macro#1{some ...
11
votes
4answers
399 views

How can I compare two (not necessarily integer) variables?

After experimenting and researching for hours, I still cannot figure out how to perform a simple equality test between two numbers. More specifically, here, the two numbers in question are the ...
11
votes
5answers
461 views

Basics of scanning

I'm trying to master the art of scanning text one character at a time. The following is what I've discovered so far. Is this as good as it gets? I would really prefer not to do all those \edefs as ...
11
votes
3answers
340 views

Expandable 'character scanning' command that preserves spaces

David Carlisle recently offered a clean and rather elegant TeX solution to a question about expandable 'character scanning' commands. Unfortunately, David's solution does not preserve spaces in the ...
11
votes
3answers
197 views

Command delimited by return or blank line

I have this document \documentclass{scrartcl} \long\def\quotenextparagraph#1 {\begin{quote}#1\end{quote}} \begin{document} Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod ...
11
votes
4answers
119 views

A question about macro matching

Consider the following macro definition, and subsequent invocation: \def\foo #1 #2 \bar{stuff with #1 and #2 goes here} \foo arg1 arg2 \bar The \bar simply acts as the terminator for \foo. This all ...
11
votes
1answer
182 views

(Re)definition of commands that use delimiters other than braces (e.g. \underbrace)

How do you go about redefining a command such as \underbrace, which uses an "uncommon" delimiter, i.e. _, between its two arguments, so that the redefined command be usable in exactly the same way as ...
11
votes
3answers
529 views

How to display only certain lines of a paragraph?

From reading Knuth's TeX Book (Chapter 14 How TeX Breaks Paragraphs into Lines), I understand that entire paragraphs are read in and then "massaged" by the "line-breaking algorithm" in an optimal way ...
11
votes
3answers
271 views

List (at run time) the macros that are currently defined

TeX of course knows at any time what control words and symbols are defined. Is it possible to access this information, for example at the end of a run? Edit: the answer for pdfTeX is no, since the ...
11
votes
1answer
354 views

Is there a \show for catcodes?

In the course of attempting to out-pedant another mathematician, I wanted to \show the catcode of $ to convince myself that it was a "special" character in ordinary TeX as well as LaTeX. I was just ...
11
votes
2answers
262 views

Determining the math class of a non-keyboard symbol

What is the "right" way of determining the math class (e.g. ordinary/0, relation/3, closing/5, etc.) of a non-keyboard symbol? Something like \oplus is easy enough to guess, but I wasn't immediately ...
11
votes
1answer
680 views

Consume/absorb a token

How does consume/absorb/remove a token from then token stream in TeX? I'm using @ifnextchar and would like to remove the character it matches.
11
votes
1answer
146 views

Begin/end a logical block?

Can I create a logical block (like HTML div element), so I can apply features like \centering locally, but not affect the outside environment?
11
votes
1answer
734 views

How to do \scantokens inside \edef without triggering “Runaway definition”

I'm trying to find a way to use the e-TeX \scantokens command inside [the equivalent of] an \edef (well, actually an \xdef, but presumably this does not make any real difference since that's just the ...
11
votes
1answer
141 views

Why this output using \string on the empty csname

How does this exactly work? \expandafter\string\csname\endcsname I don't know what I would expect to come from there, but definitely not \csname\endcsname_ where _ is a space. I thought ...
11
votes
1answer
172 views

XeTeXpicfile in vertical mode

Given a minimal like \line{% \vtop{\hsize=.6\hsize Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse tempor lectus sit amet laoreet convallis. Quisque at est lacinia, porttitor ...
11
votes
1answer
88 views

How to define a command using \lowercase in \csname

I was being lazy and had a lot of commands of the form \def\foo{...Foo...} So I was thinking about taking an approach like ...