Hi there. I've dreamed to start to write some small tricks for change the code and this is my first howto.
If you want to know how to change any another functions, you can ask us. Please, use the contact form.
For add this feature, you need to add some new code.
Please, follow the steps bellow:
1) Frontend part
Open this file - modules/mod_k2_filter/assets/js/jquery.multiselect.filter.js
Find this line:
Then, add this code bellow:
Maybe you will need to clear the browser cache for see the changes.
2) Backend part
You need to modify the filter plugin file - plugins/system/k2filter/K2Filter/models/itemlistfilter.php
Find this part of code (two match on line ~582 and line ~1658):
Then, replace this code with the following:
For extrafield type fields, you will need to modify this code (line ~2162):
And replace it with the following:
That's all. You can use it now and have fun.