OK, that doesn't work with Joomla in its present state.
Joomla does not currently support nested repeatable subforms. The subform itself can be repeatable as long as none of the fields inside of it are repeated, or the subform can contain repeatable fields as long as the subform itself is not repeated.
In Joomla 3.9.0 there is a PR to add this functionality - but it's not ready.
Give me an example of the type of data you want to store, and maybe I can tell you how to do it.
I did look and listened very carefully.
I've been playing with this whole day and I understand everything you said in the video.
BUT, you did not tell anything about multiple fields.
"The subform itself can be repeatable as long as none of the fields inside of it are repeated, or the subform can contain repeatable fields as long as the subform itself is not repeated."
I understand this as well, but I'm not trying any of these.
Let's first try to fix error in the DCMI xml and php that we talked about.
I have this repeatable field (type SUBFORM, that's tricky):
<field type="subform" name="contributor" multiple="true"
And in php it's supposed to render this way:
foreach((array)$data->contributor as $contributor) $doc->addCustomTag('<meta name="dc.contributor" content="'.htmlspecialchars($contributor).'" />');
but it's not rendering. All other (simple) fields are good, but this one returns empty. I saw in the video that you have dcmi.xml in your fields, please check.
Other one that I've been playing with is simple.
<field type="text" name="gettonet" default="" label="Gettonet" description="Opis" />
No template, multiple:true.
Renders in the article very fine in the table form. Ok, I can live with that and style it to fit me.
BUT, the point is to show it in the head metadata also!
So I'm struggling to get the output with my template so I can put in the <head> but I can't get it to work, that's where I need your (very appreciated) help.
Simply put: I need repeatable simple text field (multiple:true) that would render in the head as well wrapped by the same tag, for example: