An interesting question about Structural search "Contained in constraints" syntax

HI!

I want to find all <h3> tags in <div class="modal-body"> tags in all smarty templates in my project. With structural search i can find:

• all <h3>
• all <div class="modal-body">

But with no condition of enclosing each other or something like that. However, i find so far a predefined template, which can find "all li tags, not contained in ul or ol". I was like "wow! that's really looks like similar to my goal". Search tmeplate contains simple text:

But the interesting part is the condition, that make "not containts in ul or ol" works:

I can guess that this is works like it found all ul or ol nodes, and because "invert condition" is turned on, we get "NOT contains" but... what is this syntax? Why ONE single quote? Why "_tag"? What does it means and how it works? Can i write a similar... expression to find a tag "div" with attr "class=modal-body", to find all "h3" enclosed in?