
All field keywords beginning with html_form_ are passed directly into the form hash.
Thus,
they are really defined in form.tt which ships with Gantry.
Use html_form_raw_html if you need to put HTML directly into the entry form's table.
Your html will be immediately before the <tr> for the current field.
For it to appear in the table,
you need to wrap it in a <tr>.
Clever tricks are possible.
Remember to quote carefully.
Some experimentation might be required.

To see an example, build:
bigtop -c example.bigtop all
Change to the newly created Kids directory and look in the form method in lib/Kids/GEN/Child.pm, but run app.server and point your browser to http://localhost:8080/child/add to see the result.