docs: def style_chg_ref(self,ref,symb=None,edc=None,fac=None,smbsz=None,edw=None,lab=None):
          '''
          This routine changes the plotting style that is set by default.
          The style is changed according the the reference of the paper
          as given in the grain database. For change according to type of
          grain, use the routine syle_chg_label().
  
          ['Symbol', 'Edge color', 'Face color', 'Symbol size', 'Edge width'
          ,'Label']
  
          You can see the current styles by running
  
          Attention: You have to give values to all variables that are
          compatible with the python mathplotlib. If not, it's your fault
          if nothing works.
  
          g.style
  
          Parameters
          ----------
          ref : string
              Select the reference of the grains you want to change.
          symb : string, optional
              Select new symbol. None for no change.
          edc : string, optional
              Select new edge color. None for no change.
          fac : string, optional
              Select new face color. None for no change.
          smbsz : string, optional
              Select new symbol size. None for no change.
          edw : string, optional
              Select new edge width. None for no change.
          lab : string, optional
              Select new label. None for no change.
          '''
  
          # do stuff for selected reference
          for i in range(len(self.style)):
              # check if reference is correct, otherwise continue directly
              if self.desc[i][self.descdict['Reference']] == ref:
                  # change symbol:
                  if symb != None:
                      self.style[i][self.styledict['Symbol']] = symb
                  # change edge color
                  if edc != None:
                      self.style[i][self.styledict['Edge color']] = edc
                  # change face color
                  if fac != None:
                      self.style[i][self.styledict['Face color']] = fac
                  # change symbol size
                  if smbsz != None:
                      self.style[i][self.styledict['Symbol size']] = smbsz
                  # change edge width
                  if edw != None:
                      self.style[i][self.styledict['Edge width']] = edw
                  # change label
                  if lab != None:
                      self.style[i][self.styledict['Label']] = lab