code: def to_ds9(self, free='box',fixed='cross',frame='fk5',color='green',header=True):
          
          # todo: add support for extended sources?!
          allowed_symbols = ['circle','box','diamond','cross','x','arrow','boxcircle']
          # adding some checks.
          assert free in allowed_symbols, "symbol %s not supported"%free
          assert fixed in allowed_symbols, "symbol %s not supported"%fixed
          lines = []
          if header:
              lines.append("global color=%s"%color)
          for src in self.get_sources():
              # self.get_sources will return both Source, but also IsoSource and MapCube, in which case the sources
              # should be ignored (since they are by construction all-sky and have no corresponding ds9 region string)
              if not isinstance(src, Source): continue
              # otherwise get ra, dec
              ra, dec = src.radec
              line = "%s; point( %1.5f, %1.5f) # point=%s text={%s} color=%s"%(frame,ra, dec,
                                                                                  free if src.is_free else fixed,
                                                                                  src.name,
                                                                                  color)
              lines.append(line)
          return lines
docs: Returns a list of ds9 region definitions
          Parameters
          ----------
          free: bool
              one of the supported ds9 point symbols, used for free sources, see here: http://ds9.si.edu/doc/ref/region.html
  
          fixed: bool
              as free but for fixed sources
          
          frame: str
              typically fk5, more to be implemented
          
          color: str
              color used for symbols (only ds9 compatible colors)
          
          header: bool
              if True, will prepend a global header line.
  
          Returns
          -------
          lines : list
              list of regions (and header if requested)