check

# File lib/rexml/text.rb, line 128
    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) do
        if $1[-1] != ;;
          raise "Illegal character '#{$1}' in raw string \"#{string}\""
        elsif $1[0] == &&
          if $5 and $5[0] == ##
            case ($5[1] == xx ? $5[2..-1].to_i(16) : $5[1..-1].to_i)
            when *VALID_CHAR
            else
              raise "Illegal character '#{$1}' in raw string \"#{string}\""
            end
          # FIXME: below can't work but this needs API change.
          # elsif @parent and $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