How can I get the explanation borders with pmatrix=?iso-8859-1?Q?=3F_=96_tex.stackexchange.com?=

How can I get the explanation borders with pmatrix? – tex.stackexchange.com

I have asked this question in chat. How can I add the explanation borders
to the below matrix? \begin{align*} C_{D_{1\succ 2}, \mathrm{increasing}}
&= \underbrace{\begin{pmatrix} 1 & …