How to draw markup language structure?

Question

I want to highlight the structure of a formatting language that uses tags somewhat related to HTML, but with different capabilities regarding the closing tags. I'm thinking of something like this:

What options do I have to draw the brackets that explain the structure without the help of additional graphics software?

(I'm using pdflatex...)

Answer 1

Updated

A TikZ solution.

The implementation relies on a pair of commands \open and \close for the HTML syntax (and \openvar, \closevar for the other syntax). The commands are defined as follows:

\newcommand\open[1]{
    \tikz[remember picture,baseline=(open#1.base)]{\node(open#1){<#1>};}
}

\newcommand\close[3][red]{
    \tikz[remember picture,baseline=(close#2.base)]{
        \node(close#2){</#2>};
        \draw[#1,overlay](open#2)to[ncbar=#3](close#2);
    }
}

The -var version of the commands for the second syntax are similarly defined.

The \open command takes one argument, i.e. the name of the open tag. The \close command takes 3 arguments:

1. the first optional argument sets the color of the "bracket" connected the open and close tags (with default set to red);
2. the second argument is the name of the close tag;
3. the third argument determines the height of the "bracket". Note that the bracket is implemented by the ncbar style, provided by Jake's answer here.

Full code

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}

% ncbar style - https://tex.stackexchange.com/a/55069/18228
\tikzset{
    ncbar angle/.initial=90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=0.5cm,
}

\tikzset{every node/.style={inner sep=0pt, outer sep=0pt}} % remove unnecessary space

% HTML syntax
\newcommand\open[1]{
    \tikz[remember picture,baseline=(open#1.base)]{\node(open#1){<#1>};}
}
\newcommand\close[3][red]{
    \tikz[remember picture,baseline=(close#2.base)]{
        \node(close#2){</#2>};
        \draw[#1,overlay](open#2)to[ncbar=#3](close#2);
    }
}

% second 'unknown' syntax
\newcommand\openvar[1]{
    \tikz[remember picture,baseline=(open#1.base)]{\node(open#1){<\uppercase{#1}>};}
}
\newcommand\closevar[3][red]{
    \tikz[remember picture,baseline=(close#2.base)]{
        \node(close#2){</>};
        \draw[#1,overlay](open#2)to[ncbar=#3](close#2);
    }
}

\begin{document}

\ttfamily

\open{b} nur fett \open{i} fett kursiv \close[green]{b}{.5cm} nur kursiv \close{i}{.7cm}

\bigskip\bigskip

\openvar{b} nur Fett \openvar{i} fett kursiv \closevar{i}{.5cm}\closevar[green]{b}{.7cm}\openvar{i} nur kursiv \closevar{i}{.5cm}

\end{document}

---

Update 2

A slightly more efficient way of defining the \close command, which has only two arguments:

\newcommand\close[2][red]{
    \tikz[remember picture,baseline=(close#2.base)]{
        \node(close#2){</#2>};
        \draw[ncbar,#1,overlay](open#2)to(close#2);
    }
}

Now it only takes two arguments:

1. The first, optional argument controls the line style of the "bracket". The default is currently set to red, and maybe changed to [red,thick] to produce a red and thick line if the optional argument is not given.

   • Note also that the ncbar option is now given to the \draw operation, so by default, the height of the bracket is .5cm. If a bracket of height .7cm needs to be drawn, just use \close[ncbar=.7cm,<other options>]{<tag name>}.

2. The second argument is the same as before: the name of the close tag.

With \closevar similarly modified, the above two examples can be implemented as

\open{b} nur fett \open{i} fett kursiv \close[green]{b} nur kursiv \close[red,ncbar=.7cm]{i}

and

\openvar{b} nur Fett \openvar{i} fett kursiv \closevar{i}\closevar[green,ncbar=.7cm]{b}\openvar{i} nur kursiv \closevar{i}

Answer 2

With PSTricks just for fun. Compile it with latex-dvips-ps2pdf or xelatex (slower).

\documentclass[preview,border=24pt]{standalone}
\usepackage[T1]{fontenc}
\usepackage{pst-node}

\begin{document}
\tt
\Rnode{A}{<tag>} contents \Rnode{B}{</tag>}
\ncbar[angle=90,arm=12pt,linecolor=red]{A}{B}
\end{document}

PDFLaTeX version

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{auto-pst-pdf}
\usepackage{pst-node}


\begin{document}
This is a language:
\begin{postscript}
\tt
\Rnode{A}{<tag>} contents \Rnode{B}{</tag>}
\ncbar[angle=90,arm=12pt,linecolor=red,nodesep=6pt]{A}{B}
\end{postscript}
\end{document}