Specification in HTML

Instead of using the compact text specification with DocOnce formatting, one can use a more verbose syntax and specify everything in HTML. The second example in the section Mathematics goes as follows with HTML syntax.

 <!-- --- begin quiz --- -->
 <!-- --- begin quiz question --- -->
 The equation

 $$
 \begin{equation}
 \nabla\cdot\boldsymbol{u} = 0
 \tag{3}
 \end{equation}
 $$

 is famous in physics. Select the wrong assertion(s):
 <!-- --- end quiz question --- -->
 <!-- --- keywords:['gradient', 'divergence', 'curl', 'vector calculus'] -->
 <!-- --- label:div:assert -->

 <!-- --- begin quiz choice 1 (wrong) --- -->
 The equation tells that the net outflow of something with
 velocity \( \boldsymbol{u} \) in region is zero.
 <!-- --- end quiz choice 1 (wrong) --- -->

 <!-- --- begin explanation of choice 1 --- -->
 This is right: integrating (3) over an arbitrary
 domain \( \Omega \) and using Gauss' divergence theorem, we
 get the surface integral

 $$ \int_{\partial\Omega}\boldsymbol{u}\cdot\boldsymbol{n}dS=0,$$

 where \( \boldsymbol{n} \) is an outward unit normal on the
 boundary \( \partial\Omega \).
 The quantity \( \boldsymbol{u}\cdot\boldsymbol{n}dS \) is the
 outflow of volume per time unit if \( \boldsymbol{u} \) is
 velocity.
 <!-- --- end explanation of choice 1 --- -->

 <!-- --- begin quiz choice 2 (wrong) --- -->
 The equation tells that the vector field \( \boldsymbol{u} \)
 is divergence free.
 <!-- --- end quiz choice 2 (wrong) --- -->

 <!-- --- begin explanation of choice 2 --- -->
 Yes, <em>divergence free</em> is often used as synonym for
 <em>zero divergence</em>, and \( \nabla\cdot\boldsymbol{u} \)
 is the divergence of a vector field \( \boldsymbol{u} \).
 <!-- --- end explanation of choice 2 --- -->

 <!-- --- begin quiz choice 3 (wrong) --- -->
 The equation implies that there exists a vector potential
 \( \boldsymbol{A} \) such that
 \( \boldsymbol{u}=\nabla\times\boldsymbol{A} \).
 <!-- --- end quiz choice 3 (wrong) --- -->

 <!-- --- begin explanation of choice 3 --- -->
 Yes, this is an important result in vector calculus that is much
 used in electromagnetics.
 <!-- --- end explanation of choice 3 --- -->

 <!-- --- begin quiz choice 4 (right) --- -->
 The equation implies \( \nabla\times\boldsymbol{u}=0 \).
 <!-- --- end quiz choice 4 (right) --- -->

 <!-- --- begin explanation of choice 4 --- -->
 No, only if \( \boldsymbol{u}=\nabla\phi \), for some scalar
 potential \( \phi \), we have \( \nabla\times\boldsymbol{u}=0 \).
 <!-- --- end explanation of choice 4 --- -->

 <!-- --- begin quiz choice 5 (right) --- -->
 The equation implies that \( \boldsymbol{u} \)
 must be a constant vector field.
 <!-- --- end quiz choice 5 (right) --- -->

 <!-- --- begin explanation of choice 5 --- -->
 No, it is the <em>sum</em> of derivatives of different components
 of \( \boldsymbol{u} \) that is zero. Only in one dimension,
 where \( \boldsymbol{u}=u_x\boldsymbol{i} \) and consequently
 \( \nabla\cdot\boldsymbol{u}=du/dx \), the vector field must be
 constant.
 <!-- --- end explanation of choice 5 --- -->
 <!-- --- end quiz --- -->

This syntax applies begin-end comments to mark the start and end of the question, the choices, and the explanations.

Warning. The HTML specification of a quiz is not a meaningful HTML code for displaying the quiz in a browser, it is just an application of the HTML language to specify information and have full control of the typesetting details. Some program must interpret the HTML above and typset questions, choices, and explanations adequately.