code: def makeFeaClassName(name, existingClassNames=None):
      
      name = re.sub(r"[^A-Za-z0-9._]", r"", name)
      if existingClassNames is None:
          return name
      i = 1
      origName = name
      while name in existingClassNames:
          name = "%s_%d" % (origName, i)
          i += 1
      return name
docs: Make a glyph class name which is legal to use in feature text.
  
      Ensures the name only includes characters in "A-Za-z0-9._", and
      isn't already defined.