[Tex/LaTex] make horizontal braces over math

Question

I want to make a horizontal brace for mark a part of some numbers as special.
see the picture:
I hope I made it clear…

Answer 1

If you want the number to be not split into two parts, I suggest using pstricks, inserting empty nodes at the relevant places, and joining them by an ‘underbracket’. Here are two possibilities:

\documentclass[12pt,a4paper]{article}

\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\usepackage{pst-node}
\usepackage{auto-pst-pdf}

\begin{document}

\[\begin{postscript}
  \psset{shortput=nab, linewidth=0.5pt, arm=0.6ex, nodesep=1.5pt, labelsep=1.5pt, angle=-90}
  \pnode{a}1010\pnode{b}1010\pnode{c}
  \ncbar{a}{b}_{\textsf{\scriptsize Desc}}\ncbar[arm=1ex]{b}{c}_{\textsf{\scriptsize my desc}}
  \end{postscript}
\]
\[\begin{postscript}
  \psset{shortput=nab, linewidth=0.5pt, arm=0.6ex, nodesep=1.5pt, labelsep=1.5pt, angle=-90}
  \pnode{a}1010\pnode{b}1010\pnode{c}
  \ncbar{a}{b}_{\textsf{\scriptsize Desc}}\ncbar[angle=90, nodesep=1.8ex]{b}{c}^{\textsf{\scriptsize my desc}}
  \end{postscript}
\]
\end{document}