How create a NewDocumentCommand with ^or _?, {}^{} instead of {}{}

Question

How to create a new command with ^ or _ instead of [][][]{}{}? to be coherent/analogous with \overbracket{}^{}

Creating a new command for give color to \overbracket (mathtools package), I would like to write $\coverbracket[cyan]{x^2-2x+1}^{(x-1)^2}$ instead of $\coverbracket[cyan]{x^2-2x+1}{(x-1)^2}$

How could you code that?

\documentclass[14pt]{article}
\usepackage{mathtools}
\usepackage{xcolor}

\NewDocumentCommand{\coverbracket}{o O{2pt} O{0.7ex} m m}{
    \IfNoValueTF{#1}
    {\overbracket[#2][#3]{#4}^{#5}}
    {{\color{#1}\overbracket[#2][#3]{{\normalcolor{#4}}}^{#5}}}
}

\begin{document}
Hello, $\overbracket{x^2-2x+1}^{(x-1)^2}$

with color... $\coverbracket[cyan]{x^2-2x+1}{(x-1)^2}$
  
\end{document}

P.D.- It´s a pity that many usefull packages have no color option. Example: mathtools, ulem, ...

Answer 1

Use the e argument type:

\NewDocumentCommand{\coverbracket}{o O{2pt} O{0.7ex} m e{^}}{
    \IfNoValueTF{#1}
    {\overbracket[#2][#3]{#4}^{#5}}
    {{\color{#1}\overbracket[#2][#3]{{\normalcolor{#4}}}^{#5}}}
}

Then the new syntax of usage changes to:

$\coverbracket[cyan]{x^2-2x+1}^{(x-1)^2}$

Related post: Usage of e and E argument types in xparse?

Answer 2

I don't like the ^ or _ notations for \overbrace and similar commands. Anyway, you can use it thanks to the embellishment argument type to \NewDocumentCommand.

Your proposed syntax is unfortunately very awkward, because you can't specify the thickness and height parameters without specifying a color. Thus I move the optional color argument after the base argument and before the optional ^ part.

\documentclass{article}
\usepackage{mathtools}
\usepackage{xcolor}

\NewDocumentCommand{\coverbracket}{O{1pt} O{0.7ex} m o e{^}}{{%
  \IfNoValueTF{#4}{%
    \overbracket[#1][#2]{#3}\IfValueT{#5}{^{#5}}%
  }{%
    \colorlet{overbracketcolor}{.}%
    \mathcolor{#4}{%
      \overbracket[#1][#2]{\mathcolor{overbracketcolor}{#3}}\IfValueT{#5}{^{#5}}%
    }%
  }%
}}

\begin{document}

Hello, $\coverbracket{x^2-2x+1}^{(x-1)^2}$
and $\coverbracket[2pt]{x^2-2x+1}^{(x-1)^2}$

with color... $\coverbracket{x^2-2x+1}[cyan]^{(x-1)^2}$

with color... $\coverbracket[2pt]{x^2-2x+1}[cyan]^{(x-1)^2}$

{\color{green!70!blue} Hello $\coverbracket{x^2-2x+1}[cyan]^{(x-1)^2}$}

\bigskip

Bad: $\overbracket{xxxxx}+y$

Good: $\coverbracket{xxxxx}+y$

\end{document}

I also enclose the whole construction in a braced group (see the initial {{ and final }}): the reason should be apparent from looking at the last two lines and checking the spaces around +, which are incorrect with \overbracket, but correct with \coverbracket.

One last thing: I changed the default 2pt for the thickness into a less heavy 1pt.

Key-value syntax

You can use a single optional argument. Here an unknown key is taken as a color name. However, color= is necessary if you hide the color in a command.

If you frequently mix colors, you might want to abbreviate the key names, say to C, T and H.

\documentclass{article}
\usepackage{mathtools}
\usepackage{xcolor}

\NewDocumentCommand{\coverbracket}{O{}me{^}}{%
  {\coverunderbracket{#1}{#2}{#3}{\overbracket}{\sp}}%
}
\NewDocumentCommand{\cunderbracket}{O{}me{_}}{%
  {\coverunderbracket{#1}{#2}{#3}{\underbracket}{\sb}}%
}
\ExplSyntaxOn
\NewDocumentCommand{\coverunderbracket}{mmmmm}
 {
  \mika_bracket:nnnNN {#1} {#2} {#3} #4 #5
 }

\keys_define:nn {mika/bracket}
 {
  color     .str_set_e:N = \l_mika_bracket_color_str,
  color     .initial:n   = .,
  thickness .dim_set:N   = \l_mika_bracket_thickness_dim,
  thickness .initial:n   = 1pt,
  height    .tl_set:N    = \l_mika_bracket_height_tl,
  height    .initial:n   = 0.7ex,
  unknown   .code:n      = \tl_set_eq:NN \l_mika_bracket_color_str \l_keys_key_str
 }

\cs_new_protected:Nn \mika_bracket:nnnNN
 {% #1 = options, #2 = main formula,
  % #3 = sup/sub, #4 = \overbracket or \underbracketcommand,
  % #5 = \sp or \sb
  \keys_set:nn {mika/bracket} {#1}
  \colorlet{main_color}{.}
  \mathcolor{\l_mika_bracket_color_str}
   {
    #4
    [\l_mika_bracket_thickness_dim]
    [\l_mika_bracket_height_tl]
    {\mathcolor{main_color}{#2}}
    \tl_if_novalue:nF {#3} {#5{#3}}
   }
 }
\ExplSyntaxOff

\newcommand{\obcolor}{cyan}

\begin{document}

Hello, $\coverbracket{x^2-2x+1}^{(x-1)^2}$
and $\coverbracket[thickness=2pt,height=1ex]{x^2-2x+1}^{(x-1)^2}$

with color... $\coverbracket[color=\obcolor]{x^2-2x+1}^{(x-1)^2}$

with color... $\coverbracket[cyan,thickness=2pt]{x^2-2x+1}^{(x-1)^2}$

{\color{green!70!blue} Hello $\coverbracket[color=cyan]{x^2-2x+1}^{(x-1)^2}$}

\bigskip

Hello, $\cunderbracket{x^2-2x+1}_{(x-1)^2}$
and $\cunderbracket[thickness=2pt,height=1ex]{x^2-2x+1}_{(x-1)^2}$

with color... $\cunderbracket[color=cyan]{x^2-2x+1}_{(x-1)^2}$

with color... $\cunderbracket[color=cyan,thickness=2pt]{x^2-2x+1}_{(x-1)^2}$

{\color{green!70!blue} Hello $\cunderbracket[color=cyan]{x^2-2x+1}_{(x-1)^2}$}

\bigskip

Bad: $\overbracket{xxxxx}+y$

Good: $\coverbracket{xxxxx}+y$

\end{document}

Answer 3

Here is a use of the e type, as you're using \overbracket I've only added ^. I also add a test for contents on the ^ var, such that we avoid adding ^{} to the output when the ^ is not being used.

As for why no color support: It hasn't been something users have asked about (I personally don't see many documents that uses text with color as most people find it annoying to read). Plus it would end up giving really strange interfaces. If the macros had used key-val options to begin with, then it would probably have been easy to to add support.

\documentclass[14pt]{article}
\usepackage{mathtools}
\usepackage{xcolor}

\NewDocumentCommand{\coverbracket}{o O{2pt} O{0.7ex} m e{^}}{
    \IfNoValueTF{#1}
    {
      \overbracket[#2][#3]{#4}
      \IfNoValueF{#5}{\sp{#5}}
    }
    {
      {
        \color{#1}
        \overbracket[#2][#3]{{\normalcolor{#4}}}
        \IfNoValueF{#5}{\sp{#5}}
      }
    }
}

\begin{document}
Hello, $\overbracket{x^2-2x+1}$

 with color... $\coverbracket[cyan]{x^2-2x+1}^{(x-1)^2}$
  
\end{document}

Answer 4

\usepackage{mathtools,xcolor}

\makeatletter
% \coverbracket[<color>]{<expr>}^{<sup>}_{<sub>}  (sup/sub optional, in any order)
\newcommand{\coverbracket}[2][]{%
  \begingroup\def\cb@col{#1}%
  {\color{\cb@col}\overbracket{#2}}%
  \cb@next
}
\def\cb@next{%
  \@ifnextchar^{\cb@sup}{\@ifnextchar_{\cb@sub}{\endgroup}{\endgroup}}}
\def\cb@sup^#1{{}^{\color{\cb@col}{#1}}\cb@next}
\def\cb@sub_#1{{}_{\color{\cb@col}{#1}}\cb@next}
\makeatother

use like:

$\coverbracket[cyan]{x^2-2x+1}^{(x-1)^2}$

$\coverbracket[teal]{x^2-2x+1}_{\text{disc.}}^{(x-1)^2}$