REGEXP_LINK = "^Link:\\s*\\<(?<uri>#{URI::URI_REF})\\>" << # uri (mandatory)
                        ";\\s*rel=\"(?<rel>#{REGEXP_RESOURCE_TYPE})\"" << # rel (mandatory)
                        "(;\\s*self=\"(?<self>#{REGEXP_LINK_INSTANCE})\")?" << # self (optional)
                        "(;\\s*category=\"(?<category>(;?\\s*(#{REGEXP_LINK_TYPE}))+)\")?" << # category (optional)
                        "(?<attributes>(;?\\s*(#{REGEXP_ATTRIBUTE_REPR}))*)" << # attributes (optional)