Pull Request resolves #47451.

• 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

Fixes wrong implementation of element removal in Form->load with overwrite=false.

Testing Instructions

1. Install mod_demo47451_1.0.0.zip (System → Install → Extensions).
2. Publish the new module “Demo for issue #47451 …” in any template position
   (e.g. Cassiopeia main-top), assigned to all pages.
3. Open the site frontend.

Actual result BEFORE applying this Pull Request

Red FAIL box:

FAIL — bug #47451 present: title appears 2× in the form XML (expected 1×) and
the rendered form shows the label “Label from BASE xml (must NOT win)” — the
merge overrode the existing field in the wrong direction.

The dumped form XML contains a second <fieldset name="demo"> with a duplicate
<field name="title">.

Expected result AFTER applying this Pull Request

Green PASS box:

PASS — the existing field was kept (title appears 1× in the form XML, label:
“Label from VARIANT xml (must win)”).

The rendered fieldset shows title once with the VARIANT label, and the new
extra field from the base XML is still added correctly.

What the module does

1. Builds a Form from a variant XML that defines the field title
   (label “Label from VARIANT xml (must win)”).
2. Merges a base XML via $form->load($baseXml, false) that also defines
   title (label “Label from BASE xml (must NOT win)”) plus a new field extra.
   This mirrors what e.g. com_content's CategoryModel::preprocessForm() does
   after a variant form file was loaded.
3. Checks the result and prints a green PASS or red FAIL box, the rendered
   fieldset and the resulting form XML.

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