code: def _setSolidEdgeGeometry(self):
          
          if self._lineLengthEdge is not None:
              cr = self.contentsRect()
  
              # contents margin usually gives 1
              # cursor rectangle left edge for the very first character usually
              # gives 4
              x = self.fontMetrics().width('9' * self._lineLengthEdge) + \
                  self._totalMarginWidth + \
                  self.contentsMargins().left() + \
                  self.__cursorRect(self.firstVisibleBlock(), 0, offset=0).left()
              self._solidEdgeLine.setGeometry(QRect(x, cr.top(), 1, cr.bottom()))
docs: Sets the solid edge line geometry if needed