Is your feature request related to a problem? Please describe.

Currently if I want to use custom fields for implementing article gallery or attachments I could use something like repeatable field and then construct a subform with media field for attaching the image and text field for adding caption to that image.

However, this is pain in the a** because user has to add images one by one.

Describe the solution you'd like

Perfect solution would be to introduce concept of multi select field type from which other fields could inherit.

Inheriting from multi_select shouldn't mean that this field should necessarily always return multiple items, just that it can return multiple items if required to do so.

For example, here's how already existing fields could behave when they implement multi_select:

• media : user could select multiple files at once returning array of files
• calendar : user could select a range of dates at once returning array of dates
• user : user could select multiple users at once returning array of users

And some potential new fields that I'd also like to see:

• article : user can select multiple articles at once returning array of articles

So the idea here is that fields that implement multi_select would behave like normal single select fields as they usually do (e.g. media, user, calendar ...), but when they are within repeatable field a select box would appear above the repeatable field table allowing us to choose by which multi_select field in repeatable field we want to add new rows.

At first I thought that if there are multiple multi_select fields within the repeatable field that we should somehow select which one is "primary" but then again, why should we not be able to add new rows by any multi_select field?

Additional context

Here's the ascii layout sketch of what I'm imagining:

--------------------------------------------
| Media          ▼ | [Add New Rows Button] |
--------------------------------------------

-------------------------------------------------------------
| Image 01 [Edit] | User 01 [Edit] | Some text field 01 | [x]
-------------------------------------------------------------
| Image 02 [Edit] | User 02 [Edit] | Some text field 02 | [x]
-------------------------------------------------------------
| Image 03 [Edit] | User 03 [Edit] | Some text field 03 | [x]
-------------------------------------------------------------
| Image 04 [Edit] | User 04 [Edit] | Some text field 04 | [x]
-------------------------------------------------------------
| Image 05 [Edit] | User 05 [Edit] | Some text field 05 | [x]
-------------------------------------------------------------
| Image 06 [Edit] | User 06 [Edit] | Some text field 06 | [x]
-------------------------------------------------------------

So basically, here are two multi_select fields (media and user) within the repeatable field and a normal text field.

Before the repeatable items there is a drop down list where we can select either media or user field, and once we do we can click Add New Rows Button which will open modal where we can either select multiple files form media manager, or multiple users from user list.

When we select n users from the user list modal window we get n new rows with those selected users but all other fields empty, leaving it to the user to fill them in.

We can also change from user to media and after clicking Add New Rows Button we could add additional x rows after selecting x images.

If we try to change e.g. Image 04 from the example we get modal window again, but this time we can only select one image for that particular row in repeatable.

I think this is a good idea which would make custom fields extremely useful, but it could go to waste if we are late with adoption.

So far media manager is the main blocker for this feature because it is very bad and can't select multiple images (and files not at all) from the modal window, and he is the main feature required for creating galleries, attachments and such.