check (REXML::Text)

    # File temp/text.rb, line 129
        def Text.check string, pattern, doctype

          # illegal anywhere
          if string !~ VALID_XML_CHARS
            if String.method_defined? :encode
              string.chars.each do |c|
                case c.ord
                when *VALID_CHAR
                else
                  raise "Illegal character #{c.inspect} in raw string \"#{string}\""
                end
              end
            else
              string.scan(/[\x00-\x7F]|[\x80-\xBF][\xC0-\xF0]*|[\xC0-\xF0]/) do |c|
                case c.unpack('U')
                when *VALID_CHAR
                else
                  raise "Illegal character #{c.inspect} in raw string \"#{string}\""
                end
              end
            end
          end

          # context sensitive
          string.scan(pattern).each do
            if $1[-1] != ?;
              raise "Illegal character '#{$1}' in raw string \"#{string}\""
            elsif $1[0] == ?&
              if $5 and $5[0] == ?#
                case ($5[1] == ?x ? $5[2..-1].to_i(16) : $5[1..-1].to_i)
                when *VALID_CHAR
                else
                  raise "Illegal character '#{$1}' in raw string \"#{string}\""
                end
              elsif $3 and !SUBSTITUTES.include?($1)
                if !doctype or !doctype.entities.has_key?($3)
                  raise "Undeclared entity '#{$1}' in raw string \"#{string}\""
                end
              end
            end
          end
        end