2.3.1 Top new questions this week

2.3.1.1 Learning to use xparse

http://tex.stackexchange.com/questions/287657/learning-to-use-xparse

I'm learning to use xparse to build commands with optional arguments. But I'm having problems: 
I want to make a command called \topcat with output: 
\mathcal{O} if no argument is specified 
...
 

- asked by Abellan (14 votes), answered by Christian Hupfer (17 votes)

2.3.1.2 How to put a background letter in a table?

http://tex.stackexchange.com/questions/288087/how-to-put-a-background-letter-in-a-table

I have a table with some numbers in it, such as 
\documentclass{article} 
\begin{document} 
\begin{tabular}{llll} 
1 & 2 & 3 & 4 \\ 
1 & 2 & 3 & 4 \\ 
1 & 2 & 3 & 4 \\ 
...
 

- asked by tabular (13 votes), answered by AboAmmar (12 votes)

2.3.1.3 What all those @   resp @ \quad  in preamble of this array mean?

http://tex.stackexchange.com/questions/288067/what-all-those-resp-quad-in-preamble-of-this-array-mean

as I was reading different question This one I've found code of array enviroment which preamble is quite unknown to be... I see what it does but I would like to understand it to be able use that  ...
 

- asked by Jozef JanoA"\215ko (11 votes), answered by David Carlisle (16 votes)

2.3.1.4 How to be able to use a^\210\236 in latex document?

http://tex.stackexchange.com/questions/287795/how-to-be-able-to-use-in-latex-document

I would like to use the unicode character a^\210\236 in a LaTeX document. I use the default font. If this character is not defined in this font, I can replace it by $\infty$. 
How can I do that? 
I tried to  ...
 

- asked by Colas (10 votes), answered by David Carlisle (11 votes)

2.3.1.5 TikZ: having trouble drawing a randomly generated graph on the background of a page

http://tex.stackexchange.com/questions/288241/tikz-having-trouble-drawing-a-randomly-generated-graph-on-the-background-of-a-p

I have some code to generate random graphs: 
\documentclass{article} 
% code hijacked from:https://gist.github.com/fgrosse/5807324 
\usepackage[utf8x]{inputenc} 
\usepackage{amsmath} 
...
 

- asked by user89 (9 votes), answered by cfr (3 votes)

2.3.1.6 How Does Latex Know the Page Number of a Reference

http://tex.stackexchange.com/questions/288621/how-does-latex-know-the-page-number-of-a-reference

I am creating documents with various references, citations, an index, table of contents, and other linked elements. My question is how Latex knows how to properly cross reference a page while properly  ...
 

- asked by Steve (8 votes), answered by egreg (8 votes)

2.3.1.7 Does expl3 key-setting syntax have an equivalent of TikZ/PGF's .cd?

http://tex.stackexchange.com/questions/288272/does-expl3-key-setting-syntax-have-an-equivalent-of-tikz-pgfs-cd

This question has the following form: 'I know how to do X using Y. I can also do X using Z but not so elegantly as using Y. Can I do X using Z in the same way that I can do X using Y, for a more  ...
 

- asked by cfr (8 votes), answered by Joseph Wright (6 votes)