initialize_pattern

# File lib/uri/rfc2396_parser.rb, line 345
    def initialize_pattern(opts = {})
      ret = {}
      ret[:ESCAPED] = escaped = (opts.delete(:ESCAPED) || PATTERN::ESCAPED)
      ret[:UNRESERVED] = unreserved = opts.delete(:UNRESERVED) || PATTERN::UNRESERVED
      ret[:RESERVED] = reserved = opts.delete(:RESERVED) || PATTERN::RESERVED
      ret[:DOMLABEL] = opts.delete(:DOMLABEL) || PATTERN::DOMLABEL
      ret[:TOPLABEL] = opts.delete(:TOPLABEL) || PATTERN::TOPLABEL
      ret[:HOSTNAME] = hostname = opts.delete(:HOSTNAME)

      # RFC 2396 (URI Generic Syntax)
      # RFC 2732 (IPv6 Literal Addresses in URL's)
      # RFC 2373 (IPv6 Addressing Architecture)

      # uric          = reserved | unreserved | escaped
      ret[:URIC] = uric = "(?:[#{unreserved}#{reserved}]|#{escaped})"
      # uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" |
      #                 "&" | "=" | "+" | "$" | ","
      ret[:URIC_NO_SLASH] = uric_no_slash = "(?:[#{unreserved};?:@&=+$,]|#{escaped})"
      # query         = *uric
      ret[:QUERY] = query = "#{uric}*"
      # fragment      = *uric
      ret[:FRAGMENT] = fragment = "#{uric}*"

      # hostname      = *( domainlabel "." ) toplabel [ "." ]
      # reg-name      = *( unreserved / pct-encoded / sub-delims ) # RFC3986
      unless hostname
        ret[:HOSTNAME] = hostname = "(?:[a-zA-Z0-9\\-.]|%\\h\\h)+"
      end

      # RFC 2373, APPENDIX B:
      # IPv6address = hexpart [ ":" IPv4address ]
      # IPv4address   = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
      # hexpart = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
      # hexseq  = hex4 *( ":" hex4)
      # hex4    = 1*4HEXDIG
      #
      # XXX: This definition has a flaw. "::" + IPv4address must be
      # allowed too.  Here is a replacement.
      #
      # IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
      ret[:IPV4ADDR] = ipv4addr = "\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}"
      # hex4     = 1*4HEXDIG
      hex4 = "[#{PATTERN::HEX}]{1,4}"
      # lastpart = hex4 | IPv4address
      lastpart = "(?:#{hex4}|#{ipv4addr})"
      # hexseq1  = *( hex4 ":" ) hex4
      hexseq1 = "(?:#{hex4}:)*#{hex4}"
      # hexseq2  = *( hex4 ":" ) lastpart
      hexseq2 = "(?:#{hex4}:)*#{lastpart}"
      # IPv6address = hexseq2 | [ hexseq1 ] "::" [ hexseq2 ]
      ret[:IPV6ADDR] = ipv6addr = "(?:#{hexseq2}|(?:#{hexseq1})?::(?:#{hexseq2})?)"

      # IPv6prefix  = ( hexseq1 | [ hexseq1 ] "::" [ hexseq1 ] ) "/" 1*2DIGIT
      # unused

      # ipv6reference = "[" IPv6address "]" (RFC 2732)
      ret[:IPV6REF] = ipv6ref = "\\[#{ipv6addr}\\]"

      # host          = hostname | IPv4address
      # host          = hostname | IPv4address | IPv6reference (RFC 2732)
      ret[:HOST] = host = "(?:#{hostname}|#{ipv4addr}|#{ipv6ref})"
      # port          = *digit
      ret[:PORT] = port = '\d*'
      # hostport      = host [ ":" port ]
      ret[:HOSTPORT] = hostport = "#{host}(?::#{port})?"

      # userinfo      = *( unreserved | escaped |
      #                    ";" | ":" | "&" | "=" | "+" | "$" | "," )
      ret[:USERINFO] = userinfo = "(?:[#{unreserved};:&=+$,]|#{escaped})*"

      # pchar         = unreserved | escaped |
      #                 ":" | "@" | "&" | "=" | "+" | "$" | ","
      pchar = "(?:[#{unreserved}:@&=+$,]|#{escaped})"
      # param         = *pchar
      param = "#{pchar}*"
      # segment       = *pchar *( ";" param )
      segment = "#{pchar}*(?:;#{param})*"
      # path_segments = segment *( "/" segment )
      ret[:PATH_SEGMENTS] = path_segments = "#{segment}(?:/#{segment})*"

      # server        = [ [ userinfo "@" ] hostport ]
      server = "(?:#{userinfo}@)?#{hostport}"
      # reg_name      = 1*( unreserved | escaped | "$" | "," |
      #                     ";" | ":" | "@" | "&" | "=" | "+" )
      ret[:REG_NAME] = reg_name = "(?:[#{unreserved}$,;:@&=+]|#{escaped})+"
      # authority     = server | reg_name
      authority = "(?:#{server}|#{reg_name})"

      # rel_segment   = 1*( unreserved | escaped |
      #                     ";" | "@" | "&" | "=" | "+" | "$" | "," )
      ret[:REL_SEGMENT] = rel_segment = "(?:[#{unreserved};@&=+$,]|#{escaped})+"

      # scheme        = alpha *( alpha | digit | "+" | "-" | "." )
      ret[:SCHEME] = scheme = "[#{PATTERN::ALPHA}][\\-+.#{PATTERN::ALPHA}\\d]*"

      # abs_path      = "/"  path_segments
      ret[:ABS_PATH] = abs_path = "/#{path_segments}"
      # rel_path      = rel_segment [ abs_path ]
      ret[:REL_PATH] = rel_path = "#{rel_segment}(?:#{abs_path})?"
      # net_path      = "//" authority [ abs_path ]
      ret[:NET_PATH] = net_path = "//#{authority}(?:#{abs_path})?"

      # hier_part     = ( net_path | abs_path ) [ "?" query ]
      ret[:HIER_PART] = hier_part = "(?:#{net_path}|#{abs_path})(?:\\?(?:#{query}))?"
      # opaque_part   = uric_no_slash *uric
      ret[:OPAQUE_PART] = opaque_part = "#{uric_no_slash}#{uric}*"

      # absoluteURI   = scheme ":" ( hier_part | opaque_part )
      ret[:ABS_URI] = abs_uri = "#{scheme}:(?:#{hier_part}|#{opaque_part})"
      # relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]
      ret[:REL_URI] = rel_uri = "(?:#{net_path}|#{abs_path}|#{rel_path})(?:\\?#{query})?"

      # URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
      ret[:URI_REF] = "(?:#{abs_uri}|#{rel_uri})?(?:##{fragment})?"

      ret[:X_ABS_URI] = "
        (#{scheme}):                           (?# 1: scheme)
        (?:
           (#{opaque_part})                    (?# 2: opaque)
        |
           (?:(?:
             //(?:
                 (?:(?:(#{userinfo})@)?        (?# 3: userinfo)
                   (?:(#{host})(?::(\\d*))?))? (?# 4: host, 5: port)
               |
                 (#{reg_name})                 (?# 6: registry)
               )
             |
             (?!//))                           (?# XXX: '//' is the mark for hostport)
             (#{abs_path})?                    (?# 7: path)
           )(?:\\?(#{query}))?                 (?# 8: query)
        )
        (?:\\#(#{fragment}))?                  (?# 9: fragment)
      "

      ret[:X_REL_URI] = "
        (?:
          (?:
            //
            (?:
              (?:(#{userinfo})@)?       (?# 1: userinfo)
                (#{host})?(?::(\\d*))?  (?# 2: host, 3: port)
            |
              (#{reg_name})             (?# 4: registry)
            )
          )
        |
          (#{rel_segment})              (?# 5: rel_segment)
        )?
        (#{abs_path})?                  (?# 6: abs_path)
        (?:\\?(#{query}))?              (?# 7: query)
        (?:\\#(#{fragment}))?           (?# 8: fragment)
      "

      ret
    end