# File lib/html5/filters/validator.rb, line 640
  def check_date_time(token, tag_name, attr_name, attr_value)
    # XXX
    state = 'begin' # ('begin', '...
#    for c in attr_value
#      if state == 'begin' =>
#        if SPACE_CHARACTERS.include?(c)
#          continue
#        elsif digits.include?(c)
#          state = ...
  end