code: def _detab(self, text):
          r
          if '\t' not in text:
              return text
          return self._detab_re.subn(self._detab_sub, text)[0]
docs: r"""Remove (leading?) tabs from a file.
  
              >>> m = Markdown()
              >>> m._detab("\tfoo")
              '    foo'
              >>> m._detab("  \tfoo")
              '    foo'
              >>> m._detab("\t  foo")
              '      foo'
              >>> m._detab("  foo")
              '  foo'
              >>> m._detab("  foo\n\tbar\tblam")
              '  foo\n    bar blam'