# Daniel I. Scully

## A Beginner's Guide to MathML

### Brackets

Brackets are an essential part of maths which while serving a functional purpose also significantly improve readability. In MathML they are included with the <mfenced> tag:

1. <mfenced> 
2.  <mfrac> 
3.  <mrow> 
4.  <mi>x</mi> 
5.  <mo>+</mo> 
6.  <mn>2</mn> 
7.  </mrow> 
8.  <mn>3</mn> 
9.  </mfrac> 
10. </mfenced>
$\left(\frac{x+2}{3}\right)$

It is important (and somewhat irritating) to note that <mfenced> must contain exactly one child tag if it is simply to enclose the contents in brackets. If it contains more than one child tag, separators are inserted between them:

1. <mfenced> 
2.  <mn>3</mn> 
3.  <mn>5</mn> 
4.  <mn>4</mn> 
5. </mfenced>
$\left(3,5,4\right)$

Using the 'open', 'close' and 'separator' attributes we can specify the paretheses and separators used:

1. <mfenced open="[" close="}" separators=":"> 
2.  <mi>a</mi> 
3.  <mi>b</mi> 
4.  <mi>c</mi> 
5.  <mi>d</mi> 
6. </mfenced>
$\left[a:b:c:d\right}$

The separator attribute can also accept a list if more than one type is required (eg: separators=":~*").

As an aside targeted at my other main interest: the physicists among you will notice that this is ideally suited to the 'bra-ket' notation of quantum mechanics:

1. <mfenced open="〈" close="〉" separators="|"> 
2.  <mi>p</mi> 
3.  <mo>a</mo> 
4.  <mi>p</mi> 
5. </mfenced>
$〈p|a|\mathrm{p}〉$