https://stackoverflow.com/questions/20484738/submit-form-on-enter-key-with-javascript

Check this permission in /action/comment/add to return false if user will comment on a photo again.

You can use AJAX for this.

In UI use JS to hide comment form after adding a comment to a photo.

1. Try to use w/o 'iframe' => true
2. Your 'CSS' is your content into popup.

Sample UI for popup is:

$title = elgg_format_element('h3', ['class' => 'modal-title'], elgg_echo('Title for popup'));
$header = elgg_format_element('div', ['class' => 'modal-header'], $title);

$content = "Here is a popup content";

echo elgg_format_element('div', ['class' => 'ui-front'], $header . $content);

Thanks RvR!

1. When I use data-colorbox-opts without iframe, it throws Javascript error below:

Uncaught SyntaxError: Unexpected token < in JSON at position 0

2. I changed my code to use elgg_format_element ( ), but it does not work neither. It still returns plain HTML text in the popup.

Maybe, you need to create a view/json for this page if you're trying to fetch JSON data.

Look at responses when you load your popup (tab 'Network' in browser's DevTools).

Also, are you use json_decode() in your popup?

Perhaps, example of your summary_view could help to understand more...

There's the Profile Manager plugin (https://elgg.org/plugins/385114) which could be used to add new profile fields (can be made mandatory at account registration). But I don't think you can make conditional profile fields (i.e. depending on the selection of one field there a different additional options displayed).

The "Full age restriction checkbox" plugin (https://elgg.org/plugins/791444) is a simple plugin adding just a checkbox to the registration page. There's also no data saved (user input - or non-input - is just evaluated and either the registration proceeds or gets blocked). But maybe you could use this plugin as a starting point and just add the conditional input fields code and the data saving. Maybe the additonal profile fields could still be managed by the Profile Manager plugin (now without setting them to show on registration) as then it would automatically get them displayed on profile pages and they would be searchable.