addItem js_css explanation - Magento 1.9

Question

To add some css or js file, Magento allow different ways to do that via xml:

Add CSS file:

1- <action method="addItem"><type>skin_css</type><name>css/custom.css</name></action>

 

2- <action method="addCss"><stylesheet>css/custom.css</stylesheet></action>

 

3- <action method="addItem"><type>js_css</type><name>folder/custom.css</name></action>

Add JS file:

4- <action method="addItem"><type>skin_js</type><name>js/custom.js</name></action>

 

5- <action method="addJs"><script>folder/custom.js</script></action>

Now my question is:

In the line 3 what is js_css ? from what I understood, it is to add css but why we don't add it in css/ file with all files css skin/frontend/package/theme/css/ instead of js/

Answer 1

This is for JavaScript libraries that bundle their CSS together like many sliders/scrollers do. For example slick (https://github.com/kenwheeler/slick).