This would have the JS Popup Window replaced with a Modal DIV element.

[MarkoKrsic]

Replaces JS popup window with JS Modal DIV, browser stays on product screen/page.
This would replace additional_images.php in includes/modules/ and tpl_modules_main_product_image.php in the includes/templates/template_default/templates/

[Zen4All]

IMHO the styles and javascripts should go in their seperate files, instead of including them in the php file.

[MarkoKrsic]

IMHO the styles and javascripts should go in their seperate files, instead of including them in the php file.

I agree and knew I forgot something right after I submitted just didn't have time yet to circle back to it.

I am also not sure where to place them for best conformity to existing project standards? Should I put the CSS in the base includes/templates/template_default/css/stylesheet.css? If not where do I declare and include it?

JS in jscript folder?

I am willing to split it all out but would you be willing to place/conform it to standard?

[dbltoe]

Since it is going to be part of the core, I would use the existing stylesheets.
For add-ons and customizations, we add stylesheet_zcustom.css to most of our projects so we can find the code when upgrade time comes.

[lat9]

I take my thumbs-up back. Since that CSS requires 'programmatic' inserts, I'll suggest creating a .php file in the /templates/template_default/css directory that does the insertions and creating a like-named file in the /templates/responsive_classic/css directory that requires the template_default version (so there's really only one file to be maintained).

Each template's /common/html_header.php would specifically load the file in its /css subdirectory.

[drbyte]

Oops. I was trying to update the branch, and github closed it.

I'll push it as a separate PR, giving @MarkoKrsic commit credit.