def levels(self):
        _levels = RstHeaderTree.DEFAULT_HEADERS.copy()
        for h in self.headers:
            _levels[h.level] = h.adornment
        levels = []
        for adornment in _levels:
            if adornment not in levels:
                levels.append(adornment)
        for adornment in RstHeaderTree.DEFAULT_HEADERS:
            if adornment not in levels:
                if len(adornment) == 2:
                    levels.insert(0, adornment)
                else:
                    levels.append(adornment)
        return levels
returns the heading adornment map
dataset/ETHPy150Open mgaitan/sublime-rst-completion/headers.py/RstHeaderTree.levels