Collapsed tree rendering

Notes about collapsed tree rendering

(top-level-parent ...)
(parent expression (...)
 (parent expression (...)
  (parent expression (...)
   (prev-prev-sibling) .. (pp-sibling)
   (prev-sibling form...
     ... prev sibling last-child form)
   (Current-expression
     ...
     ...
     ...
     ... last child form)
   (next-sibling-expression ...)))
(next-parent expresssion ...
(next-perent expression)
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1/3 prev-sibling/parent

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1/3 current-expression

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1/3 next-sibling/parent

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