Properties file:Comments.properties
  PsiComment(Properties:END_OF_LINE_COMMENT)('# xxx')
  PsiWhiteSpace('\n')
  PropertiesList
    Property:xx
      PsiElement(Properties:KEY_CHARACTERS)('xx')
      PsiElement(Properties:KEY_VALUE_SEPARATOR)('=')
      Property value: yyy('yyy')
  PsiWhiteSpace('\n')
  PsiComment(Properties:END_OF_LINE_COMMENT)('#s')