:has Relational Pseudo-Class
      
      Oxygen XML Editor supports the CSS Level 4 subject selector (currently a working draft
            at W3C http://www.w3.org/TR/selectors4/), as
            described in Subject Selector. Oxygen XML Editor also supports the :has relational pseudo-class that has similar
            functionality and it can match an element by taking its child elements into account.
            For more
            information, see https://drafts.csswg.org/selectors-4/#relational.
         
You can create conditions that take into account the structure of the matching element.
table:has( tbody > thead){
 border: 1px solid red;
}This example
            will result in a border being drawn for the table elements that contain at least a
            thead element in the tbody element.
         Taking Processing Instructions into Account in CSS Subject Selectors
You can test for the existence of specific processing instructions (PI) in
               the child hierarchy of a subject selector.
            
For example:
@namespace oxy "http://www.oxygenxml.com/extensions/author";
chapter! > oxy|processing-instruction[important][level="high"]{
  color:red;
}
            
            This would change the color of a DocBook chapter to red if it contains the
               important processing
               instruction:
<chapter> <title>A title</title> <?important level='high'?> </chapter>
Descendant Selectors Limitation
Important
a! b cand:
a! > b > c
