URI::RFC2396_Parser#split

# File tmp/rubies/ruby-3.0.5/lib/uri/rfc2396_parser.rb, line 120
def split(uri)
  case uri
  when ''
    # null uri

  when @regexp[:ABS_URI]
    scheme, opaque, userinfo, host, port,
      registry, path, query, fragment = $~[1..-1]

    # URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]

    # absoluteURI   = scheme ":" ( hier_part | opaque_part )
    # hier_part     = ( net_path | abs_path ) [ "?" query ]
    # opaque_part   = uric_no_slash *uric

    # abs_path      = "/"  path_segments
    # net_path      = "//" authority [ abs_path ]

    # authority     = server | reg_name
    # server        = [ [ userinfo "@" ] hostport ]

    if !scheme
      raise InvalidURIError,
        "bad URI(absolute but no scheme): #{uri}"
    end
    if !opaque && (!path && (!host && !registry))
      raise InvalidURIError,
        "bad URI(absolute but no path): #{uri}"
    end

  when @regexp[:REL_URI]
    scheme = nil
    opaque = nil

    userinfo, host, port, registry,
      rel_segment, abs_path, query, fragment = $~[1..-1]
    if rel_segment && abs_path
      path = rel_segment + abs_path
    elsif rel_segment
      path = rel_segment
    elsif abs_path
      path = abs_path
    end

    # URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]

    # relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]

    # net_path      = "//" authority [ abs_path ]
    # abs_path      = "/"  path_segments
    # rel_path      = rel_segment [ abs_path ]

    # authority     = server | reg_name
    # server        = [ [ userinfo "@" ] hostport ]

  else
    raise InvalidURIError, "bad URI(is not URI?): #{uri}"
  end

  path = '' if !path && !opaque # (see RFC2396 Section 5.2)
  ret = [
    scheme,
    userinfo, host, port,         # X
    registry,                     # X
    path,                         # Y
    opaque,                       # Y
    query,
    fragment
  ]
  return ret
end