Gdddk

This question is something of a follow-up to tex4ht: customize includegraphics conversion to HTML and also to When generating html, how do you specify image size?

background

In my .tex file I specify images to be included as follows:

includegraphics[alt=alt tags, information]example-image-a

and have theimg element wrapped in its own container:

<div class="figure"><!--l. 7-->
<p class="noindent"></p>
<div class="my-box"><img src="mwe0x.png" alt="PIC" class=
"my-class" /></div>
<!--l. 8-->
<p class="indent"></p>
</div>

I use the following cmh.cfg:

Preamblehtml5
makeatletter
define@keyGinalt
ConfigureGraphicsAltmy alt text
Configuregraphics
 HCode<div class="my-box">%
 Picture+[PIC] class="my-class"
 EndPicture HCode</div>
begindocument
EndPreamble

and produce the html output above using the call:

make4ht -u -f html5 -c cmh.cfg mwe.tex

goal

I'd like to have the ALT tag updated from the includegraphics call.

I've tried the following modification to cmh.cfg

Picture+[a:GraphicsAlt] class="my-class"}

but this results in

Missing $ inserted

the question

How can I change my cmh.cfg file so that the img element receives custom alt tags and my custom class?

mwe.tex

documentclassarticle
usepackagegraphicx
begindocument

here is some text
beginfigure
 includegraphics[alt=descriptions,info]example-image-a
endfigure
enddocument

cmh.cfg

Preamblehtml5
makeatletter
define@keyGinalt
ConfigureGraphicsAltmy alt text
Configuregraphics
 HCode<div class="my-box">%
 Picture+[PIC] class="my-class"
 EndPicture HCode</div>
begindocument
EndPreamble

call

make4ht -u -f html5 -c cmh.cfg mwe.tex

I would use a following configuration file:

Preamblexhtml
makeatletter
DeclareGraphicsExtensions.png,.jpg,.svg
define@keyGinaltConfigureGraphicsAlt#1
defmygraphicsConfigureNeedsFile: Gin@baseGin@extNeeds%
 ifvmodeIgnoreParfiEndPHCode<div class="my-box">Picture[csname a:GraphicsAltendcsname]Gin@baseGin@ext csname a:Gin-dimendcsname class="my-class" 
HCode</div>ShowPar
Configuregraphics*
 png
 mygraphics
Configuregraphics*
 jpg
 mygraphics
Configuregraphics*
 jpeg
 mygraphics
Configuregraphics*
 svg
 mygraphics

begindocument

EndPreamble

The DeclareGraphicsExtension is used to declare graphics filetypes supported in HTML. The mygraphics macro contains common code inserted for graphics, especially dimensions, alt and class. It is then used in configurations for supported graphics types, so we can save some repetition. The alt text is declared by define@keyGinaltConfigureGraphicsAlt#1.

You also need to copy the example-image-a.png file to the current directory and save its dimensions using ebb -x example-image-a.png command.

The result:

<!--l. 8--><p class="noindent" >here is some text </p><figure class="figure"> 



<!--l. 10--><p class="noindent" ></p><div class="my-box"><img 
src="example-image-a.png" alt="descriptions,info" 
width="401" height="301" class="my-class" /></div>

 </figure>