[5.4] Fix regex pattern in ShowOnRule for custom fields

[LadySolveig]

Pull Request resolves # .

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

As it is a valid condition in the XML form for the showon attribute to have something like foo: to display a field only if another field is empty, this should also be possible via the custom fields.

Testing Instructions

1. Add two custom fields in Articles: Fields (text or textarea - doesn't matter)

2. Add foo: as showon rule into the field in the options tab

3. Additional tests

• using various combinations of fields, such as Select, etc
• OR conditions such as foo:[OR]foo:0 or foo:0[OR]foo:
• check whether other conditions are working as before
• test the other way around foo!: - the bar field should now only be displayed if the foo field is not empty

Actual result BEFORE applying this Pull Request

Rejected by validation.

Expected result AFTER applying this Pull Request

Can be saved and works the same way just like we've been doing all along, by inserting directly into the XML form

The bar field will now only be displayed if the foo field is empty.

ssitdocker.test_j54_administrator_index.php_option.com_content.view.articles.Laptop.2026-03-25.18.04.09.mp4

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[richard67]

3. Additional tests

* using various combinations of fields, such as Select, etc

* `OR` conditions such as `foo:[OR]foo:0` or `foo:0[OR]foo:`

* check whether other conditions are working as before

@LadySolveig Maybe another additional test for a condition !foo: would be useful to see if that is not broken?

I know, it is covered by the last point "check whether other conditions are working as before".

But maybe it should be explicitly mentioned?

[exlemor]

I have tested this item ✅ successfully on 6e0e00b

I have tested this successfully... Thanks @LadySolveig! (solving useful things I didn't know we had in Joomla ;) )

I also tested foo:[OR]foo:0 or foo:0[OR]foo: and foo!: which all worked as expected.

@richard67 I assume you meant foo!: and not !foo: (as !foo: did yield the same error message of Invalid field: Showon Attribute) while foo!: saved and behaved in the expected opposite manner of foo:

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[krishnagandhicode]

I have tested this item ✅ successfully on 6e0e00b


Everything works as expected(also verified the edge cases - foo!: and foo:[OR]foo:0, and they saved perfectly).

On a personal note: I recently learned about regular expressions in my Formal Theory of Automata course, so seeing this regex fix in action is really cool.

Thanks @LadySolveig : )

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[LadySolveig]

Thank you for testing it, @exlemor and @krishnagandhicode! 💚

I really appreciate your personal note. Keep that curiosity and open-mindedness!
The great thing about open source is that throughout our lives, we’ll keep coming across exciting things that we’d previously only heard about in theory.

[richard67]

RTC

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[muhme]

✅ Final test before merge with JBT

• Seen error before,
• Created text1, text2 and text3
• Tested text3 showon attributes 'text1:', 'text1!:', text1:[OR]text1:0 and 'text1!:[OR]text2!:'

[muhme]

Thank you @LadySolveig for your contribution. Thank you @richard67 for support. Thank you @exlemor and @krishnagandhicode for testing.