Note that this allows for integration with KnockoutJS, Angularjs, etc.

Can you a bit more specific what the purpose of this change would be? And how it could be tested?

@Bakual
Sometimes could be useful pass the object from html element to the javascript code

$array = ['id' => 12345, 'title' => 'Some title', 'someMore' => '...'];

<input type="..." data-some-object="<?php echo htmlspecialchars(json_encode($array), ENT_QUOTES, 'UTF-8'); ?>" />

var data = $('#element-id').data('some-object');
console.log(data.someMore);

This change looks like you would specify that object data in the form XML file. I don't see yet the global need for that. I think it's simpler to just extend the formfield and add your specific requirements into it.
Having a preg_match running on each list element attribute when it's used only in a few very specific cases looks wrong to me.

I think this better do in the field layout override, if you need it .. in J 3.5 it should be even more easy

@dbclkclk please can you fix the code style errors

FOUND 17 ERROR(S) AFFECTING 9 LINE(S)

47 | ERROR | Functions and classes must not contain multiple empty lines in a
| | row; found 2 empty lines
49 | ERROR | Tabs must be used to indent lines; spaces are not allowed
50 | ERROR | Tabs must be used to indent lines; spaces are not allowed
51 | ERROR | Tabs must be used to indent lines; spaces are not allowed
51 | ERROR | Expected "if (...)\n...{...}\n...else\n"; found
| | "if(...)\n...{...}\n...else\n"
52 | ERROR | Tabs must be used to indent lines; spaces are not allowed
53 | ERROR | Tabs must be used to indent lines; spaces are not allowed
53 | ERROR | Concat operator must be followed by one space
53 | ERROR | Concat operator must be preceeded by one space
53 | ERROR | Concat operator must be followed by one space
53 | ERROR | Concat operator must be preceeded by one space
53 | ERROR | Concat operator must be followed by one space
53 | ERROR | Concat operator must be preceeded by one space
54 | ERROR | Tabs must be used to indent lines; spaces are not allowed
55 | ERROR | Tabs must be used to indent lines; spaces are not allowed
55 | ERROR | Closing brace indented incorrectly; expected 3 spaces, found 16
56 | ERROR | Functions and classes must not contain multiple empty lines in a
| | row; found 2 empty lines

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_{This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/9463.}

This PR will be closed in a few weeks if the code style issues are not resoled

@dbclkclk @brianteeman see dbclkclk#1

@wojsmol , @dbclkclk

This is nice to have, there are many uses of data-* attributes

• many developers extend JFormFieldList and add this

Some comments

if (preg_match('(data-[a-zA-Z\-]+)', $a))

• does not allow number in name which is legitimate: data-somename1=""
• does not allow legimate Unicode characters

why would not trust the developer has created a proper names in the XML file ?

1 . So i think better just use:

if (preg_match('(data-)', $a))

2 . Also this is 2x faster

if ( strpos($a, 'data-') === 0 ) 

Example for 500,000 calls aka 500,000 list fields (<select>)

0,15ms versus 0,30ms on same processor

• so it is not really needed, unless someone in the future decides to add in similar way data- attributes in the <option>

I am closing this at this time as it cannot be merged in its current state and there has been no response to the request to update the code. It can always b reopened if that is done.