Thanks for your question. I regret that the short answer is no, the Search Media feature of the Media/Assistant submenu does not support complex queries of the type you give as examples. It is a “keyword search” modeled after the WordPress search features.
Your first example, “Title starts with AB* and Att. Categories is empty” can be approximated by selecting “No Att. Categories” in the dropdown box at the top of the table and clicking “Apply”, then doing a Search Media on “AB”. You will get some false matches but the results may be close enough to let you sort through the items to find the ones you want.
Your second example, ‘Att. Categories is different than “Audi” and “Mercedes”‘ could be done by creating an [mla_gallery] shortcode with a tax_query parameter to select the items you want.
I realize this is inconvenient at best and may not work for you, but that’s all I can suggest with the current MLA version. If this is an important feature for your application you could use the “Media/Assistant Submenu Actions and Filters (Hooks)” to build a more powerful and flexible solution, but the work required would be significant.
I am marking this topic resolved, although I regret that the news is not better. Thanks for your interest in the plugin.
