“header_format” not accepting HTML tags

I use your plugin on several sites, and I am very satisfied.

However, there is a problem with the “header_format” parameter in connection with a grouped list.

The page in question (cf. link) has a tabbed menu with 6 tabs, of which tabs 2-5 each contain results filtered by an event tag which defines the local organizer. I would now like to add a link to the group heading (i.e. month), which in this special case should create a PDF file providing a printable event list for the respective organizer in the respective month. However, tab 1 must not have such a link, which is why the global settings cannot be used.

I tried to solve the problem using the “header_format” parameter, which, in your documentation, is (incorrectly?) defined as “bool”. The source code (public static function output_grouped) however suggests to me that text could be entered there in spite of that definition. In fact, using the shortcode “events_list_grouped”, any text is actually displayed; “#s” is also replaced as described in the documentation, but HTML tags are not observed, and are only displayed as text. So, including an additional link (“<a href=”) isn’t working.

Perhaps I misunderstand something here — or is it a bug? Any advice is appreciated.

The page I need help with: [log in to see the link]