code: def parseTopDepth(self, descendants=()):
          
          descendants = list(descendants) or \
              list(getattr(self.source, 'descendants', descendants))
          if not descendants:
              return -1
          return min(TOC.getHeadingLevel(e, self.hierarchy) for e in descendants)
docs: Parse tex for highest tag in hierarchy
  
          >>> TOC.fromLatex('\\section{Hah}\\subsection{No}').parseTopDepth()
          1
          >>> s = '\\subsubsubsection{Yo}\\subsubsection{Hah}'
          >>> TOC.fromLatex(s).parseTopDepth()
          1
          >>> h = ('section', 'subsubsection', 'subsubsubsection')
          >>> TOC.fromLatex(s, hierarchy=h).parseTopDepth()
          2