Questions tagged [tex-core]

{tex-core} is for questions for syntax, semantics and expected behavior of TeX primitive control sequences, regardless of extensions (eTeX, etc.) formats (Plain or LaTeX) and macro packages (tikz). 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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188 votes
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Escape character in LaTeX

I need to output the below text but since \ is a special character, I cannot: [RegularExpression(@"\d+")] Also sometimes I need use dollar sign $ as well but it seems to be a special char, too. ...
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119 votes
4 answers
52k views

How to check if a macro value is empty or will not create text with plain TeX conditionals?

I have a macro which holds some text value, e.g. \macro{some text}. If it is empty, I would like for nothing to appear in the document, but it has some content of any kind which would produce text ...
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214 votes
5 answers
60k views

When to use \edef, \noexpand, and \expandafter?

I'm quite happy hacking TeX macros and cobbling together bits and pieces from different style files to suit my own ends, but I have a suspicion that my resulting hacks are not quite as elegant as they ...
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244 votes
9 answers
108k views

What is the difference between TeX and LaTeX?

I know LaTeX and I've heard that LaTeX is a set of macros in TeX. But what does it exactly mean?
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110 votes
2 answers
17k views

The differences between TeX engines

I am confused about what TeX and its offspring (LaTeX, pdfTeX/pdfLaTeX, e-TeX, ConTeXt, LuaTeX, etc.) are. Some, like LaTeX, seem like add ons to TeX (maybe a change to the eyes and mouth, but not ...
163 votes
10 answers
124k views

How to expand TeX's "main memory size"? (pgfplots memory overload)

I'm compiling one pretty simple LaTeX file with few dozen of pgfplots. Now, I can compile part by part, but am unable to compile it all at once. I really need good precision for all those plots (noise ...
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189 votes
6 answers
49k views

What exactly do \csname and \endcsname do?

What exactly do \csname and \endcsname do? What are their job? I have glanced at the Texbook and some other books, but none of them was clear enough to me. Can anyone please give a simple example to ...
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60 votes
1 answer
7k views

What do different \fontdimen<num> mean

I know that \fontdimen<num> returns some dimensions associated with the current font. What are they?
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103 votes
5 answers
13k views

Is there a BNF grammar of the TeX language?

I'm looking for a BNF grammar of the TeX language, does it exist? EDIT For those of us who are not computer scientists, a BNF grammar is one kind of formal description of a CFG: Backus Naur Form. ...
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71 votes
4 answers
8k views

What are category codes?

Following on from this question, I'd like to ask a more general question: What are category codes, and what can I achieve by changing them?
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155 votes
2 answers
29k views

What are penalties and which ones are defined?

Very often you can find solutions by changing the penalty. One is widowpenalty. However what are penalties and is there a small list of every defined penalty. There is a German site which does ...
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251 votes
3 answers
65k views

What is the difference between \let and \def?

What is the difference between the \let and \def commands in TeX/LaTeX? Ideally please provide a simple example that will illustrate the difference between them.
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  • 9,804
28 votes
4 answers
2k views

How to properly smuggle (with or even without TikZ)?

I am seeking to find something that allows me to "broadcast" macros outside a group. Concrete examples include paths and scopes in tizpictures. Here is an M(N)WE. \documentclass[tikz,border=3.14mm]{...
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36 votes
2 answers
4k views

Why can words with hyphen char not be hyphenated?

Assume I have a word like Baden-Württemberg. TeX can't hyphenate any of these two word parts. Why? why isn't it something like this: where the small ticks indicate possible hyphenation points. A ...
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22 votes
5 answers
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Basics of parsing

I'm trying to master the art of parsing 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 ...
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  • 70.9k
130 votes
3 answers
12k views

What is the difference between \relax and {}?

As I understand it, the point of \relax is to stop a macro from swallowing up subsequent material (such as whitespace). But {} (\bgroup\egroup) serves the same function. Why do we need both?
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75 votes
4 answers
3k views

Advantages and disadvantages of fully expandable macros

As I currently understand them, fully-expandable macros are analogous to pure/effect-free functions in functional programming. Correspondingly, things that are not expandable, such as \def, are ...
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81 votes
3 answers
3k views

Why isn't everything expandable?

TeX's macro processor does its work in a process called expansion. For an input stream of tokens, the macro processor repeatedly expands them until non-expandable tokens remain. The resulting stream ...
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41 votes
1 answer
2k views

The \lowercase trick

We have a number of questions or rather answers using (and explaining) the \lowercase “trick”. \begingroup \lccode`\~=`\. \lowercase{\endgroup\def~}#1{foo with #1} However, after reading on ...
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67 votes
6 answers
27k views

How to form "if ... or ... then" conditionals in TeX?

I feel really stupid for asking this, but how do you form more complex if conditionals in TeX? I'm looking for something like: \ifnum\x=1 OR \ifnum\x=14 {do this} \else {do that} \fi I don't ...
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70 votes
10 answers
12k views

What is the best way to learn TeX?

As opposed to LaTeX, which is addressed in another question. Most of the references I've seen get too complex too quickly. I'm looking for something that gives me a top-down view of the language - ...
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  • 3,453
56 votes
5 answers
10k views

Confused with TeX terminology: height, depth, width

The LaTeX reference card states for example \strut box w/ ht and depth of “(”, zero width I came to see text as a two dimensional feature, but I must be missing out on something... (following was ...
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71 votes
1 answer
4k views

What are the incompatibilities of pdftex, xetex and luatex?

[Please correct me if my statements are wrong] TL;DR: pdftex, xetex and luatex exhibit different behaviour. What are these differences and why are they present. I know of three engines, which ...
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12 votes
3 answers
4k views

Showing Solutions of the Questions "separately"

There is a class for LaTeX called exam. Using this class, one can write questions and answers for exams. The answers are displayed under (after) each question. My goal is to have all answers in the ...
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194 votes
23 answers
12k views

Are there any open research problems in the world of TeX?

For a year-long capstone project in computer science, I have to do some 'original research.' I'm still not entirely sure what this entails, but it just struck me that perhaps I can do research and ...
135 votes
2 answers
49k views

When should one use \begingroup instead of \bgroup?

Is there ever a case when the use of \begingroup is preferred to \bgroup? Obviously, \bgroup is necessary in cases where you need to have balanced braces and thus cannot use {, but when is it ...
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68 votes
5 answers
6k views

What are TeX and LaTeX?

I'm surprised no one else has asked this question. It's not explained very well in the FAQ or site descriptions either. I know many of you will think "LMGTFY", "RTFM", or "ask wikipedia", but I'd ...
88 votes
4 answers
27k views

What is the difference between 'fil' and 'fill'?

TeX provides the commands \vfil and \vfill (and their corresponding horizontal versions \hfil and \hfill). These commands are actually defined as: \vskip 0cm plus 1fil \vskip 0cm plus 1fill where '...
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44 votes
2 answers
3k views

Why does a TeX point differ from a Desktop Publishing point?

From this answer to Why does PDFLaTeX and XeLaTeX generates 11.955 font size for 12pt documentclass option?, I found out that PDF and TeX have different ideas about the size of the point (pt). A TeX ...
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48 votes
3 answers
2k views

How to implement (low-level) arrays in TeX

Update: I have revised my question based on the comment by Bruno Le Floch and some further research. As some may know, I'm implementing a huge TeX macro package which has to do a lot of internal ...
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34 votes
2 answers
2k views

How does TeX look for delimited arguments?

The following code \def\foo#1#2\baz{\#1: -#1- \quad \#2: -#2-} 1) \foo hello world\baz 2) \foo supercalifragilistiexpialidocious\baz 3) \foo a \baz 4) \foo a\baz %5) \foo \baz % error! \bye ...
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72 votes
4 answers
7k views

What is "expansion"?

I'm relatively new to (La)TeX, but I have a reasonable amount of experience with computational programming languages. Until I began learning (La)TeX, I'd never heard of "expansion"... So, what is "...
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77 votes
4 answers
18k views

What is the difference between \let and \edef?

When you write \edef\a{\b} \let\a\b the results are often identical. What is the difference between these two commands? When do they behave the same? When do they not? (The question isn't for me; ...
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29 votes
5 answers
3k views

Showcase of brace tricks: }, \egroup, \iffalse{\fi}, etc.

There have been a few questions about braces recently, specifically about when to use them (see this and that question). Note: I had mistakenly stated that SamB was the author of both questions. But ...
16 votes
2 answers
3k 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, ...
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  • 1,073
17 votes
1 answer
8k views

TeX capacity exceeded (save size)

I am generating a fairly large index of .txt, .tex, and .pdf files. This process has worked for a long time, and the size of the index is not the issue. I have added logic to insert additional links ...
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89 votes
3 answers
38k views

Difference between \if and \ifx

I try to understand the subtleties of TeX programming, but it is not always easy. For example, in the following code : \def\first{abc} \def\second{abc} \ifx\first\second OK!\else false \fi I ...
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  • 3,482
62 votes
2 answers
9k views

What is the basic mechanism for writing something to an aux file?

I am interested in the basic mechanism behind writing stuff to the .aux file. (Or some other auxiliary file). Let's say I want to write myself a basic package for making notes on my files. (I know ...
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  • 70.6k
44 votes
2 answers
14k views

What are the exact semantics of \detokenize?

How does \detokenize work? The e-TeX Short Reference Manual states: When followed by a <general text>, expands to yield a sequence of character tokens of \catcode 10 (space) or 12 (...
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  • 7,891
28 votes
7 answers
3k views

Are there purely expandable variants of \MakeUppercase?

\MakeUppercase and \uppercase use TeX's uccode, and they are not purely expandable. Say, \edef\temp{\MakeUppercase{abc}} will fail. Sometimes purely expandable macros are very useful. They are ...
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  • 74.5k
56 votes
1 answer
31k views

formal syntax rules of \dimexpr \numexpr \glueexpr

After looking at various answers on the site and by looking at the documentation of e-tex, I am still wondering what is exactly allowed in the various types of expressions, i.e. \numexpr, \dimexpr and ...
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34 votes
4 answers
2k views

Display hyphenation options for a specific word

When TeX produces Overfull box, is puts something like this in the log: Overfull \hbox (15.47195pt too wide) in paragraph at lines 7--9 []\OT1/cmr/m/n/10 I re-ally re-ally want to get dis-played the ...
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  • 49.2k
33 votes
2 answers
6k views

Components of (La)TeX's memory usage

After reading Increase LaTeX capacity and not being able to summon Gandalf1, I am curious to know what contributes to the components of memory usage during a (La)TeX compilation. Take the above post's ...
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  • 570k
21 votes
3 answers
2k 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 ...
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  • 15.3k
20 votes
3 answers
7k 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 ...
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17 votes
3 answers
3k views

How can I open a file in "append" mode?

Could not find anything in the TeXBook, but this could be just me. I guess it is always possible to open the file for reading, copy its content to another file, and then continue writing to that file....
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  • 15.3k
17 votes
1 answer
6k views

Origin and formation to the ERROR ‘Dimension too large’

When I tried to compile: \documentclass{standalone} \usepackage{tikz} \begin{document} \begin{tikzpicture} \draw[very thin, red] (0,0) circle (2); \foreach \i in {0, 1, 2, ..., 46} \draw[very thin, ...
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  • 3,743
9 votes
3 answers
492 views

Appending active and expansion sensitive characters to a macro

This question comes up pretty often when people want to build tables with empty columns or similarly building up some active characters inside a macro hoping to expand them at the right time right ...
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  • 154k
172 votes
4 answers
539k views

\vspace vs. \vskip [duplicate]

What is the difference between \vspace{-1em} and \vskip -1em, for example? I guess the first is LaTeX, and the latter is TeX. When is the proper time to use one and not the other, and why?
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  • 3,561
138 votes
8 answers
34k views

Why are there no alternatives to TeX, or, why is TeX still used? [closed]

I'm fairly new to TeX and LaTeX, having been drawn in by the Big Idea — creating a document programmatically. However, my experience of TeX (and its libraries — LaTeX, ConTeXt, …) has been almost ...
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