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http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33762&start=0

Tested. The group name is shown now, but I think $item_heading should be removed, since it has no effect and there's no possibility to declare it.

yes, but not remover $item_heading :(
set in default.php
<<?php echo $item_heading; ?>><?php echo $group_name; ?></<?php echo $item_heading; ?>>
and in modules/mod_articles_category/mod_articles_category.php
line 72 from
$item_heading = $params->get('item_heading');
to
$item_heading = $params->get('header_tag');

and now you can use the advanced parameter "Header Tag" in the module admin

I think a solution like the one in mod_article_news is better. Then you can use $item_heading.

I'm sorry but I don't know the solution in mod_article_news. But if it is better is ok :)

Okay :)

It's possible to specify the item_heading:

<field
name="item_heading"
type="list"
default="h4"
label="MOD_ARTICLES_NEWS_TITLE_HEADING"
description="MOD_ARTICLES_NEWS_TITLE_HEADING_DESCRIPTION">
<option value="h1">JH1</option>
<option value="h2">JH2</option>
<option value="h3">JH3</option>
<option value="h4">JH4</option>
<option value="h5">JH5</option>
</field>

but also in the Module Articles Category is possible to specify the item_heading:

<option value="h1">h1</option>
<option value="h2">h2</option>
<option value="h3">h3</option>
<option value="h4">h4</option>
<option value="h5">h5</option>
<option value="h6">h6</option>
<option value="p">p</option>

I don't if I'm blind, but I can't find that in the xml file :(

Yes it is not in the xml file, but it is in the advanced parameter of the module admin and in the database. But if you prefer edit the xml and insert the new item_heading parameter is ok. I think you can also leave the same language string.

The pull request for the mod_articles_category.php file
#3626

Closed as per the comment on joomlacode