What is Author-Level Markup?

The question arises in the context of the question of whether HTML extended by MathML is suitable for authors.

I believe that most mathematical authors find it much easier to create the LaTeX version of given content than to create the corresponding HTML content. Unfortunately, if translation from LaTeX to HTML is to be done well, profiled use of LaTeX is required.

Let me illustrate with a simple example involving markup for setting the formula for the roots of a quadratic polynomial.

Author-Level Markup This can be done with generalized LaTeX under “regular GELLMU”, which is very close to classical LaTeX, as follows:

\documenttype{article}
\title{Quadratic Formula}
\begin{document}
 
In a field of characteristic other than $2$ the roots of the
quadratic polynomial $ax^2 + bx + c$ with $a \neq 0$ are:
\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]
\end{document}

HTML with Math So that we are comparing “apples” with “apples”, this is formulated as generalized LaTeX under “basic GELLMU” using the markup vocabulary of HTML and MathML with LaTeX-like syntax:

\documenttype[]{html}
\newcommand{\imath}[1]{\math[mode="inline"]{#1}}
\newcommand{\dmath}[1]{\math[display="block" mode="display"]{#1}}
\begin{head}
\link[rel="stylesheet" type="text/css" href="../webstyle/mxh.css"]
\meta[charset="UTF-8"]
\title{Quadratic Formula}
\script[type="text/javascript"
src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"
       ]{}
\end{head}
\begin{body}
\h1[class="display"]{Quadratic Formula}
\begin{p}
In a field of characteristic other than \imath{\mn{2}}
the roots of the quadratic polynomial
\imath{\mi{a}\msup{\mi{x}\mn{2}}\mo{+}\mi{b}\mi{x}\mo{+}\mi{c}}
with \imath{\mi{a}\mo{≠}\mn{0}} are:
\dmath{
\mi{x}\mo{=}
\mrow{\mfrac{
        \mrow{\mo{−}\mi{b}\mo{±}
          \msqrt{\msup{\mi{b}\mn{2}}\mo{−}\mn{4}\mi{a}\mi{c}}}
        \mrow{\mn{2}\mi{a}}}}
}
\end{p}
\end{body}

These two sources yield lead to essentially the same MathJax-enabled HTML document: the first version and the second version.