What additional formatting features are available to MathJax (possibly via \require{})?

Question

In his answer to a question about crossing out units in dimensional analysis, Loong notes that the \cancel{} LaTeX command can be enabled in MathJax by using \require{cancel} at the start of a MathJax block.

What other commands/features can be enabled in MathJax through the use of \require{}, or other similar MathJax-internal commands?

---

Peter's answer points to the MathJax documentation, which lists the additional features available using \require{}. Many of these features are sufficiently cool and potentially useful that I want to make them more visible. So, I plan to lay out the available features and examples of their usage in the answers below. For convenience, below is a table of contents—you may want to wait to click these until the page has fully loaded and all of the MathJax has rendered, otherwise the entry you want may "run away" from you:

• 2-D Reaction Networks – \require{AMScd}

• Cancellation Lines – \require{cancel}

• Coloring (CSS-Style) – \bbox

• Coloring ($\mathrm\LaTeX$-Style) – \require{color}

• Command Grouping – \require{begingroup}

• Extensible Arrows – \require{extpfeil}

• mediawiki-texvc Symbols – \require{mediawiki-texvc}

• Links and CSS Styling/Formatting – \href, \style, \class, \cssId

• Overlay/Enclosure Annotations – \require{enclose}

• Tooltips and Toggleable Math – \require{action}

• Unicode Characters – \unicode

To note, even though mhchem has been enabled on Chem.SE by default, it is not enabled on many other sites in the Stack Exchange network. If for some reason you have need of chemical equations somewhere else and \ce isn't rendering properly for you, including \require{mhchem} should make it work. Per the developer's comment and chat post, though, beware that sites that do not specifically load the newest mhchem will load whatever version is packaged with the current version of MathJax, and therefore some behavior may differ, possibly significantly.

The amsmath and amssymbols extensions are also enabled by default on Chem.SE. The symbols available by default, as well as those that require activation by \require{mediawiki-texvc}, can be browsed at the relevant section of the MathJax documentation. In particular, if you are interested in using the symbol for Angstrom units, use \AA after supplying \require{mediawiki-texvc}:

$$ \require{mediawiki-texvc} \AA $$

Finally, note that using any of these \require{} commands will enable the feature set for the entire webpage in which they will appear. This shouldn't be a problem for most the commands laid out here; the primary exception is \require{color}, which will interfere with any uses of the default $\mathrm\TeX$ form of \color{}. As such, \bbox is preferred, when possible. There do exist a couple of additional MathJax extensions not listed above that can be loaded with \require{}, but I've omitted them here because they will essentially always have significant side-effects beyond just the post in which they're included.

Answer 1

As described in the MathJax documentation, any of the core MathJax extensions can be loaded this way (though this can be restricted via the MathJax configuration).

Answer 2

Command Grouping

Enable with: \require{begingroup}

Environment: \begingroup ... \endgroup

Quite a few things are possible with MathJax when you set your mind to it. For example you can define new commands with \newcommand{...}. In order to preserve default behaviour for the other posts, you might want enclose your post in a group with \require{begingroup}. $\require{begingroup}$

As a result you can use the following code without destroying our nice site for the next post.

$$
\begingroup
\newcommand{\op}[1]{\mathbf{#1}}
\op{H}\Psi=E\Psi \tag{mathbf}\label{schrödi1}
\endgroup
$$
$$
\begingroup
\newcommand{\op}[1]{\hat{#1}}
\op{H}\Psi=E\Psi \tag{hat}\label{schrödi2}
\endgroup
$$ 

Which gives us: $$ \begingroup \newcommand{\op}[1]{\mathbf{#1}} \op{H}\Psi=E\Psi \tag{mathbf}\label{schrödi1} \endgroup $$ $$ \begingroup \newcommand{\op}[1]{\hat{#1}} \op{H}\Psi=E\Psi \tag{hat}\label{schrödi2} \endgroup $$

Note that labels added with \label{} still have to be unique regardless of grouping: $\eqref{schrödi1}$ and $\eqref{schrödi2}$. Also, note that using \begingroup .. \endgroup does not contain the effects of loading other packages: once loaded, a package affects the entire page.

Answer 3

2-D Reaction Networks

Enable with: \require{AMScd}

Environment: \begin{CD} ... \end{CD}

Construct two-dimensional grids connected with single-headed arrows. Double-headed and double-lined arrows appear not to be supported, unfortunately. mwchem (\ce{...}) is supported, but you have to apply it to each item in the grid, not the entire grid as a single item.

Annotations above/below/beside the arrows are indicated by interleaving them into the codes for the arrows:

Up:      @AAA
Down: @VVV
Left:    @<<<
Right: @>>>

Double-lines can be used, but unfortunately without arrowheads:

Vertical:      @|||
Horizontal: @===

Anywhere a 'non-arrow' needs to be inserted, @. can be used.

More information is available in the PDF here.

$$
\require{AMScd}
\begin{CD}
\ce A         @>k_1>>    \ce B         @.         ~       \\
@Vk_2VV                  @VVk_4V                  @.      \\
\ce C         @>k_3>>    \ce D         @<k_5<<    \ce E   \\
@Ak_7AA                  @VVk_6V                  @.      \\
\ce G         @.         \ce F         @.         ~       \\
\end{CD}
$$

$$ \require{AMScd} ~\\ \begin{CD} \ce A @>k_1>> \ce B @. ~ \\ @Vk_2VV @VVk_4V @. \\ \ce C @>k_3>> \ce D @<k_5<< \ce E \\ @Ak_7AA @VVk_6V @. \\ \ce G @. \ce F @. ~ \\ \end{CD} $$

Answer 4

Cancellation Lines

Enable with: \require{cancel}

Commands: \cancel{}, \bcancel{}, \xcancel{}, \cancelto{}

Overstrike math content with:

• \cancel:     A diagonal line rising to the right
• \bcancel:   A diagonal line falling to the right
• \xcancel:   An 'X'
• \cancelto: A single-headed arrow rising to the right, with a value indicated at the end of the arrow

 

$$
\require{cancel}
{\cancel{x} y \over \cancel{x}} = y \\
{x^\bcancel{3} \over \cancel{x^2}} = x \\
\xcancel{0 = 1} \\
\cancelto{\,5}{25 \over 5}
$$

$$ \require{cancel} ~\\ {\cancel{x} y \over \cancel{x}} = y \\ {x^\bcancel{3} \over \cancel{x^2}} = x \\ \xcancel{0 = 1} \\ \cancelto{\,5}{25 \over 5} $$

Answer 5

Tooltips and Toggleable Math

Enable with: \require{action}

Commands: \mathtip{math}{tip} and \texttip{math}{tip}

Apply tooltips to math expressions (text shown when the cursor is hovered over the expression). \mathtip shows tip using math-mode rendering; \texttip shows tip using text-mode rendering.

$$
\require{action}
\texttip{a+b}{This is addition!} \\ ~ \\
\mathtip{\ln{\!\left( e^x \right)}}{=x}
$$

$$ \require{action} ~\\ \texttip{a+b}{This is addition!} \\ ~ \\ \mathtip{\ln{\!\left( e^x \right)}}{=x} $$

---

Command: \toggle{math1}{math2}...\endtoggle

Create a math object that cycles through different expressions when clicked.

$$
\require{action}
\toggle{a}{a+b}{a+b+c}{a+b+c+d}\endtoggle
$$

$$ \require{action} ~\\ \toggle{a}{a+b}{a+b+c}{a+b+c+d}\endtoggle $$

Answer 6

Overlay/Enclosure Annotations

Enable with: \require{enclose} $\require{enclose}$

Command: \enclose{type}[options]{math}

Apply a MathML 3 enclosure, with optional text or background color formatting (see here for available color descriptors), to math.

Available enclosures include:

• longdiv - Long division symbol (it's apparently possible to construct entire long division problems; I did not take the time to figure out how, though)
   
  \enclose{longdiv}[mathcolor="red"]{x^2+5} $\rightarrow \enclose{longdiv}[mathcolor="red"]{x^2+5}$
   

• actuarial - Symbol from actuarial notation (no particular relevance to chemistry)
   
  \enclose{actuarial}[mathbackground="#6ad898"]{2x} $\rightarrow \enclose{actuarial}[mathbackground="#6ad898"]{2x}$
   

• phasorangle - Phasor angle symbol (also no particular relevance to chemistry):
   
  A_1\enclose{phasorangle}{\theta_1} $\rightarrow A_1\enclose{phasorangle}{\theta_1}$
   

• radical - Root symbol
   
  ^3\enclose{radical}{x^6} = x^2 $\rightarrow~^3\enclose{radical}{x^6} = x^2$
   

• box - Box with hard corners
   
  \enclose{box}{x = 1 \pm 3} $\rightarrow \enclose{box}{x = 1 \pm 3}$
   

• roundedbox - Box with rounded corners
   
  \enclose{roundedbox}{y = {1\over x}} $\rightarrow \enclose{roundedbox}{y = {1\over x}}$
   

• circle - Ellipse (ironically); may have to include extra horizontal or vertical whitespace to avoid clipping
   
  \enclose{circle}{f(x)=x^2} $\rightarrow \enclose{circle}{f(x)=x^2}$
  \enclose{circle}{~~~~f(x)=x^2\phantom{x^2\over 1}} $\rightarrow \enclose{circle}{~~~~f(x)=x^2\phantom{x^2\over 1}}$
   

• left, right, top, bottom - Line on one side of the math
   
  \enclose{bottom}{x+y}\cdots\enclose{right}{x\over y} $\rightarrow\enclose{bottom}{x+y}\cdots\enclose{right}{x\over y}$
   

• updiagonalstrike, downdiagonalstrike,
  verticalstrike, horizontalstrike - Strikethroughs
   
  \enclose{verticalstrike}{a+b^2\over c+d}$\rightarrow\enclose{verticalstrike}{a+b^2\over c+d}$
  \enclose{updiagonalstrike}{a+b^2\over c+d}$\rightarrow\enclose{updiagonalstrike}{a+b^2\over c+d}$
   

• madruwb - Arabic factorial (renders an approximation on my browser)
   
  enclose{madruwb}{55} $\rightarrow\enclose{madruwb}{55}$
   

Multiple enclosures can be applied to the same math by passing a space-separated list of enclosures to \enclose:

      \enclose{circle updiagonalstrike horizontalstrike}{y^3 - xy^2} $\rightarrow\enclose{circle updiagonalstrike horizontalstrike}{y^3 - xy^2}$

At this time (5 Feb 2017) it appears that MathJax does not implement the arrows defined in the MathML specification (northeastarrow, updownarrow, etc.) except for updiagonalarrow (thanks, Davide!):

      \enclose{updiagonalarrow}{3x^2} $\rightarrow\enclose{updiagonalarrow}{3x^2}$

Answer 7

Unicode Characters

Enable with: \require{unicode} (optional; loads automatically on first use)

Command: \unicode{#####} or \unicode{x####}

Insert the Unicode character at decimal code point ##### or hexadecimal code point x####. As usual, proper rendering depends on browser encoding support. There are many resources for Unicode code points around the Internet; searching "Unicode [thing]" will frequently point you in the right direction. I discovered this site recently, which has a nice categorized listing of an extremely large set of Unicode code points.

Examples

Fractions

From here and here:

$ \require{begingroup} \begingroup \newcommand{graybox}[1]{\bbox[whitesmoke,1px]{\texttt{x#1}}} ~~~~~~~~\begin{array}{ccccccc} \hline \graybox{00bd} & \graybox{2153} & \graybox{2154} & \graybox{00bc} & \graybox{00be} \\ \unicode{x00bd} & \unicode{x2153} & \unicode{x2154} & \unicode{x00bc} & \unicode{x00be} \\ \hline \graybox{2155} & \graybox{2156} & \graybox{2157} & \graybox{2158} & \graybox{2159} & \graybox{215a} \\ \unicode{x2155} & \unicode{x2156} & \unicode{x2157} & \unicode{x2158} & \unicode{x2159} & \unicode{x215a} \\ \hline \graybox{2150} & \graybox{215b} & \graybox{215c} & \graybox{215d} & \graybox{215e} & \graybox{2151} & \graybox{2152} \\ \unicode{x2150} & \unicode{x215b} & \unicode{x215c} & \unicode{x215d} & \unicode{x215e} & \unicode{x2151} & \unicode{x2152} \\ \hline \end{array} $

 
Geometric Shapes

A few examples from here:

$\unicode{x25a0}~~\unicode{x25a1}~~\unicode{x25aa}~~\unicode{x25b7}~~\unicode{x25c1}~~\unicode{x25bd}~~\unicode{x25cb}~~\unicode{x25cf}~~\unicode{x25d0}~~\unicode{x25d7}~~\unicode{x25d8}~~\unicode{x25e2}~~\unicode{x25e8}~~\unicode{x25ea}~~\unicode{x25ed}$

 
Punctuation

Examples from here:

$\unicode{x2032}~~\unicode{x2033}~~\unicode{x2034}~~\unicode{x2016}$

And from here:

$\unicode{x00a1}~~\unicode{x00bf}~~\unicode{x00a7}~~\unicode{x00ab}~~\unicode{x00bb}~~\unicode{x00b0}~~\unicode{x00a9}~~\unicode{x00ae}$

 
Currency Symbols

Examples from here:

$\unicode{x20ac}~~\unicode{x20b9}~~\unicode{x20bd}~~\unicode{xfdfc}$

And from here:

$\unicode{x00a2}~~\unicode{x00a3}$

 
Arrows

Examples from here:

$\unicode{x2192}~~\unicode{x2194}~~\unicode{x2197}~~\unicode{x219b}~~\unicode{x219d}~~\unicode{x21a0}~~\unicode{x21a6}~~\unicode{x21aa}~~\unicode{x21ac}~~\unicode{x21b3}~~\unicode{x21b7}~~\unicode{x21c0}~~\unicode{x21c4} \\ \unicode{x21c9}~~\unicode{x21cc}~~\unicode{x21cf}~~\unicode{x21d2}~~\unicode{x21d7}~~\unicode{x21dd}~~\unicode{x21e2}~~\unicode{x21e5}~~\unicode{x21f0}~~\unicode{x21f2}~~\unicode{x21f6}~~\unicode{x21f8}~~\unicode{x21fb}~~\unicode{x21fe}$

 
Mathematical Operators/Symbols

Examples from here:

$\unicode{x00d7}~~\unicode{x00f7}~~\unicode{x00b1}$

And from here:

$\unicode{x2030}~~\unicode{x2031}$

And from here:

$\unicode{x2200}~~\unicode{x2203}~~\unicode{x2208}~~\unicode{x2213}~~\unicode{x221e}~~\unicode{x2220}~~\unicode{x2227}~~\unicode{x2229}~~\unicode{x2234}~~\unicode{x2243}~~\unicode{x2245}~~\unicode{x2250}~~\unicode{x2273}$

$\endgroup$

Answer 8

mediawiki-texvc Symbols

Enable with: \require{mediawiki-texvc}

Commands: (various)

As noted in the question, the full set of symbols exposed through the mediawiki-texvc extension can be browsed at the MathJax documentation. Many of these symbols are (or appear to me to be) one-to-one substitutions for commands already available in MathJax as it is presently configured on Chem.SE.

Included in the table below are a subset of the mediawiki-texvc symbols of particular note, either because they are unavailable in the default Chem.SE MathJax or because their mediawiki-texvc commands are appreciably shorter and/or clearer. Some are not of particular relevance to chemistry, but are included for the possible benefit of users from (GASP) other sites in the SE network.

$ \require{mediawiki-texvc} \require{begingroup} \begingroup \def\grbx#1{\bbox[2pt,lightgray,font-size:75%]{\text{#1}}} \def\smx{--} $

$ \begin{array}{cccccc} \hline {\small\text{Default}} & \grbx{\spadesuit} & \grbx{\heartsuit} & \grbx{\diamondsuit} & \grbx{\clubsuit} \\ {\small\text{mediawiki-texvc}} & \grbx{\spades} & \grbx{\hearts} & \grbx{\diamonds} & \grbx{\clubs} \\ {\small\text{Symbol}} & \spades & \hearts & \diamonds & \clubs \\ \hline {\small\text{Default}} & \grbx{\mathbb{C}} & \grbx{\mathbb{H}} & \grbx{\mathbb{N}} \\ {\small\text{mediawiki-texvc}} & \grbx{\C} & \grbx{\H} & \grbx{\N} \\ {\small\text{Symbol}} & \C & \H & \N \\ {\small\text{Default}} & \grbx{\mathbb{Q}} & \grbx{\mathbb{R}} & \grbx{\mathbb{Z}}\\ {\small\text{mediawiki-texvc}} & \grbx{\Q} & \grbx{\R} & \grbx{\Z} \\ {\small\text{Symbol}} & \Q & \R & \Z \\ \hline {\small\text{Default}} & \grbx{\rightarrow} & \grbx{\Rightarrow} & \grbx{\leftrightarrow} & \grbx{\Leftrightarrow} \\ {\small\text{mediawiki-texvc}} & \grbx{\rarr} & \grbx{\Rarr} & \grbx{\lrarr} & \grbx{\Lrarr} \\ {\small\text{Symbol}} & \rarr & \Rarr & \lrarr & \Lrarr \\ \hline {\small\text{Default}} & \smx & \smx & \smx & \smx \\ {\small\text{mediawiki-texvc}} & \grbx{\coppa} & \grbx{\Koppa} & \grbx{\sampi} & \grbx{\Sampi} \\ {\small\text{Symbol}} & \coppa & \Koppa & \sampi & \Sampi \\ {\small\text{Default}} & \smx & \smx & \grbx{\vartheta} \\ {\small\text{mediawiki-texvc}} & \grbx{\stigma} & \grbx{\Stigma} & \grbx{\thetasym} \\ {\small\text{Symbol}} & \stigma & \Stigma & \thetasym \\ \hline {\small\text{Default}} & \grbx{\subset} & \grbx{\subseteq} & \grbx{\supset} & \grbx{\supseteq} \\ {\small\text{mediawiki-texvc}} & \grbx{\sub} & \grbx{\sube} & \smx & \grbx{\supe} \\ {\small\text{Symbol}} & \sub & \sube & \supset & \supe \\ {\small\text{Default}} & \grbx{\land} & \grbx{\lor} \\ {\small\text{mediawiki-texvc}} & \grbx{\and} & \grbx{\or} \\ {\small\text{Symbol}} & \and & \or \\ \hline {\small\text{Default}} & \smx & \smx & \smx \\ {\small\text{mediawiki-texvc}} & \grbx{\AA} & \grbx{\euro} & \grbx{\textvisiblespace} \\ {\small\text{Symbol}} & \AA & \euro & \textvisiblespace \\ {\small\text{Default}} & \smx & \grbx{\wp} \\ {\small\text{mediawiki-texvc}} & \grbx{\vline} & \grbx{\weierp} \\ {\small\text{Symbol}} & \vline & \weierp \\ \hline \end{array} $

Note that \vline and the pipe symbol are not the same:
 
   \vline – $\vline$
   {pipe} – |

$\endgroup$

Answer 9

Coloring ($\rm\LaTeX$ Style)

Enable with: \require{color}

Commands: \color (redefinition), \colorbox, \fcolorbox, \definecolor, \textcolor

MathJax ships by default with a non-standard implementation of the \color command, which applies a case-insensitive predefined or svgnames color to some math passed to it as an argument:

$$
\color{reD}{x+y}+z = \color{bLUe}{m^2} \\
\color{NAVY}{\ce{HCl}}~~\color{MedIUMSEaGREeN}{\ce{NaCl}}
$$

$$ {\color{reD}{x+y}}+z = {\color{bLUe}{m^2}} \\ {\color{NAVY}{\ce{HCl}}}~~{\color{MedIUMSEaGREeN}{\ce{NaCl}}} $$

---

Invoking \require{color} loads a much broader set of commands. First, \color is overwritten, turning it into a to-end-of-scope modifier instead of a pure command that takes the material to be colored as an argument:

$$
\require{color}
\color{red}{this} that \\
{or \color{red} this} that
$$

$$ \require{color} \color{red}{this} that \\ {or \color{red} this} that $$

This redefinition applies to everything parsed after the \require invocation, page-wide. It thus has the potential to break uses of the default argument-based \color in other posts on the page!

---

A command with the argument-coloring behavior, \textcolor, is defined:

$$
\textcolor{RED}{this} that
$$

$$ \textcolor{RED}{this} that $$

---

The case-sensitive dvipsnames color space is loaded:

$$
\textcolor{Apricot}{noodle} \\
{this \color{Thistle} that} other {\color{thistle} wise}
$$

$$ \textcolor{Apricot}{noodle} \\ {this \color{Thistle} that} other {\color{thistle} wise} $$

The difference in color above is due to $\color{Thistle}that$ being colored with dvipsnames case-sensitive "Thistle" but $\color{thistle}wise$ being colored with svgnames case-insensitive "Thistle"/"thistle".

---

New color names can be defined with \definecolor in a variety of ways:

$$
\definecolor{mygray2!}{gray}{0.4}
\definecolor{clay}{rgb}{0.8,0.32,0.0}
\definecolor{newBlue21}{RGB}{25,65,180}
~
\textcolor{mygray2!}{12345}~\textcolor{MyGray2!}{67890} \\
\textcolor{clay}{whiplash}~\textcolor{cLAy}{sagebrush} \\
\textcolor{newBlue21}{undertow}~\textcolor{newblue21}{no~good}
$$

$$ \definecolor{mygray2!}{gray}{0.4} \definecolor{clay}{rgb}{0.8,0.32,0.0} \definecolor{newBlue21}{RGB}{25,65,180} ~ \textcolor{mygray2!}{12345}~\textcolor{MyGray2!}{67890} \\ \textcolor{clay}{whiplash}~\textcolor{cLAy}{sagebrush} \\ \textcolor{newBlue21}{undertow}~\textcolor{newblue21}{no~good} $$

Color names defined with \definecolor are strictly case-sensitive. It appears that as of this writing the HTML and cmyk color models described at the above link are not available.

---

Text highlighting and framed text highlighting are provided by \colorbox and \fcolorbox, respectively. Font coloring is not available as a direct argument to either command, and the contents of both of these commands are set as plain text, not as mathematics or formatted $\rm\LaTeX$. If desired, though, math (and thus full $\rm\LaTeX$ formatting, including text coloration) can be included by surrounding the relevant portions in the typical dollar signs:

$$
\colorbox{clay}{$\textcolor{SkyBlue}{\text{This is text.}}$} \\
\fcolorbox{burlywood}{mygray2!}{$\textcolor{Goldenrod}{This~is~\mathbf{framed}~math~text.}$}
$$

$$ \colorbox{clay}{$\textcolor{SkyBlue}{\text{This is text.}}$} \\ \fcolorbox{burlywood}{mygray2!}{$\textcolor{Goldenrod}{This~is~\mathbf{framed}~math~text.}$} $$

Answer 10

Links and CSS Styling/Formatting

Enable with: \require{html} (optional; loads automatically on first use)

Commands: \href, \class, \cssId, \style

\style allows (nearly) arbitrary CSS formatting to be applied to a math (sub-)expression. Per usual CSS syntax, separate individual CSS directives by semicolons. w3schools.com has a pretty good CSS tutorial.

$$
\style{color: blue}{a+b}+\style{padding: 3pt; background-color: green}{c+d}
$$

$$ \style{color: blue}{a+b}+\style{padding: 3pt; background-color: green}{c+d} $$

Much the same effect can be achieved with the \bbox command. As with \bbox, the output is only well-behaved if a numerical pixel value is explicitly supplied for border-width:

$$
\style{border-style: solid; border-width: 5px; padding: 2px}{x^2-3x+2}
$$

$$ \style{border-style: solid; border-width: 5px; padding: 2px}{x^2-3x+2} $$

Nesting \style directives can also have dramatic side effects. For example, when drafting this post, I managed to create a math expression that made the webpage page "infinitely long", and totally blank below the CSS-formatted math expression. (For what are hopefully obvious reasons, I removed this expression from the final version of the post....) I hadn't yet discovered the need for explicitly specifying the border-width property to avoid misbehavior at that point, though, so it's possible this weirdness stemmed from that same problem.

---

Unfortunately, the remaining three commands supplied by this extension are somewhat useless on Stack Exchange. Per a comment by Peter Krautzberger, \href, which would allow construction of links within math expressions, appears to be disabled on SE sites for security reasons. Instead of creating a link, the URL is just echoed into the expression:

\href{http://www.google.com}{a+b}

$$\href{http://www.google.com}{a+b}$$

In theory, \class would permit formatting arbitrary MathJax expressions with the same styles applied to the 'native' Stack Exchange CSS classes. Considering that 2002 was the last time I worked directly with CSS, I have not had success in extracting class names from the SE .css file. (Alternatively, it is possible that \class has also been disabled by the SE developers.) If anyone can get this command to work, please feel free to edit instructions into this answer.

\cssId, which attaches an id attribute to a math (sub-)expression, is of little use on Stack Exchange since to my knowledge post authors don't have the ability to modify the CSS or Javascript running on the site.

Answer 11

Extensible Arrows

Enable with: \require{extpfeil}

Commands: \xtwoheadrightarrow, \xtwoheadleftarrow, \xmapsto, \xlongequal, \xtofrom, \Newextarrow

Create an arrow with overset content, sized to fit that content. Five built-in arrows are defined, of which four work properly in my browser: $\require{begingroup}\begingroup\def\rar{\quad\longrightarrow\quad}\require{extpfeil}$

• \xtwoheadrightarrow{a+b+c}: $\quad\xtwoheadrightarrow{a+b+c}$

• \xtwoheadleftarrow{a+b+d+c}: $\quad\xtwoheadleftarrow{a+b+d+c}$

• \xmapsto{\text{This is a real, actual sentence.}}: $\quad\xmapsto{\text{This is a real, actual sentence.}}$

• \xlongequal{\text{extremely long equals sign}}: $\quad\xlongequal{\text{extremely long equals sign}}$

I have not been able to get \xtofrom to work:

• \xtofrom{ax^2+bx+c=0}: $\quad\xtofrom{ax^2+bx+c=0}$

A variety of other extensible arrows can be crafted with this extension, via the \Newextarrow{\cmd}{lspace,rspace}{unicode-char} command. Here, \cmd is the name of the new command to be defined, lspace and rspace are integers defining the left and right padding, respectively, for the text to be overset (in units of pixels?), and unicode-char is the Unicode code point for the arrow to be typeset in extended form. To note, unicode-char must be specified in hexadecimal, and must be prefixed by 0x (not just x). For example:

$$
\Newextarrow{\xtriple}{10,10}{0x21db}
\Newextarrow{\xtriplepadded}{50,50}{0x21db}
\xtriple{\text{This is an extended triple arrow!}} \\
\xtriplepadded{\text{This is an extended triple arrow with lots of padding!}}
$$

$$ \Newextarrow{\xtriple}{10,10}{0x21db} \Newextarrow{\xtriplepadded}{50,50}{0x21db} \xtriple{\text{This is an extended triple arrow!}} \\ \xtriplepadded{\text{This is an extended triple arrow with lots of padding!}} $$

The following table lays out all of the arrows I have observed to work with \Newextarrow; three of these are duplicates of the arrows built into the extension. Conspicuously absent (for now?), unfortunately, is the equilibrium reaction arrow, 0x21cc $(\unicode{x21cc})$.

$$ \newcommand{graybox}[1]{\bbox[whitesmoke,1px]{\texttt{0x#1}}} \begin{array}{cccccc} \hline \graybox{2190} & \graybox{2192} & \graybox{2194} & \graybox{21d0} & \graybox{21d2} & \graybox{21d4} \\ \unicode{x2190} & \unicode{x2192} & \unicode{x2194} & \unicode{x21d0} & \unicode{x21d2} & \unicode{x21d4} \\ \hline \graybox{21bc} & \graybox{21c0} & \graybox{294e} & \graybox{21bd} & \graybox{21c1} & \graybox{2950} \\ \unicode{x21bc} & \unicode{x21c0} & \unicode{x294e} & \unicode{x21bd} & \unicode{x21c1} & \unicode{x2950} \\ \hline \graybox{219e} & \graybox{21a0} & \graybox{21a4} & \graybox{21a6} & \graybox{295a} & \graybox{295b} \\ \unicode{x219e} & \unicode{x21a0} & \unicode{x21a4} & \unicode{x21a6} & \unicode{x295a} & \unicode{x295b} \\ \hline \graybox{295e} & \graybox{295f} & \graybox{27fd} & \graybox{27fe} & \graybox{21da} & \graybox{21db} \\ \unicode{x295e} & \unicode{x295f} & \unicode{x27fd} & \unicode{x27fe} & \unicode{x21da} & \unicode{x21db} \\ \hline \end{array} $$ $\endgroup$

Answer 12

Coloring (CSS-Style)

Enable with: \require{bbox} (optional; loads automatically on first use)

Command: \bbox[options]{math}

\bbox is somewhat similar to \style, in that it applies CSS styling to the indicated math. The main difference is that it makes two specific assumptions about unqualified CSS directives passed into options:

1. An unqualified (case-insensitive) CSS or svgnames color is taken as the background-color:

          \bbox[cyan]{a+b} $\quad\rightarrow\quad \bbox[cyan]{a+b}$

2. An unqualified CSS distance measurement is taken as the padding:

          \bbox[10px,cyan]{a+b} $\quad\rightarrow\quad \bbox[10px,cyan]{a+b}$

As shown above, these unqualified CSS directives are separated by a comma.

Arbitrary CSS styling (w3schools.com has a pretty good tutorial) can also be applied to the math, regardless of the presence or absence of the above unqualified directives, by providing a series of semicolon-separated full CSS directives:

\bbox[lightblue,5px,border-style: solid; border-color:greenyellow; border-width: 4px]{a+b}

          $\rightarrow\quad \bbox[lightblue,5px,border-style: solid; border-color:greenyellow; border-width: 4px]{a+b}$

IMPORTANT: If you specify a border around the math, in order for the MathJax to render correctly you MUST supply at minimum both the border-style and border-width properties. Further, the border-width property must be specified as a pixel value (e.g., 4px). If you omit border-style, no border will be drawn. If you omit border-width or supply it as a relative-size keyword (e.g., thick), the text will be misaligned to the box and, on some browsers, will mess up the alignment of all following MathJax on the page!

ADDENDUM: From DavideCervone's comment:

Note that it is easier to give the combined version for borders, e.g., border: 4px solid greenyellow rather than giving each part separately. Finally, you can give the width in values other than pixels (e.g., 2em or 3mm), but you are correct that it must be an explicit width, not a keyword like thick in order for MathJax to be able to compensate for it properly.