====National Classifications====
GN and HN are subdivided by nations. Two-letter codes are used for nations represented in the current TLD list found online at [https://en.wikipedia.org/wiki/List_of_Internet_topCountry_code_top-level_domainslevel_domain#Country_code_top-level_domains Lists Wikipedia]. (This source is preferred as there are a number of competing agencies and standards.) Nations not represented on this list are assigned two character cutter codes. Note that this results in nations being shelved out of strict alphabetical order (sometimes wildly so, as Switzerland uses CH).
New codes will be assigned as needed, using the Internet's Top Level Domain (TLD ) list where possible, and Cutter numbers where not.
Country codes in use include:
|B9 = Byzantine Empire||FR = France||JO = Jordan||R6 = Rome
|-
|BB = Barbados||rowspan=2|G7 = Great Britain<br> (see also E6, IM, S3, <br> UK, W3)||JP = Japan||RU = Russia
|-
|BE = Belgium||LT = Lithuania||S3 = Scotland
|CA = Canada||GT = Guatemala||M6 = Moravia||SZ = Swaziland
|-
|CH = Switzerland||H3 = Hawai'’i (as a nation)||MC = Monaco||rowspan=2|UK = United Kingdom<br> (see also E6, G7, IM, <br> S3, W3)
|-
|CN = China||H6 = Holy Roman Empire||MM = Myanmar (Burma)
|-
|CU = Cuba||HU = Hungary||MX = Mexico||rowspanUA =2|US = United States<br> (see also State codes)Egypt
|-
|DE = Germany||IL = Israel||N3 = Naples||rowspan=2|US = United States<br> (see also State<br> codes)
|-
|DK = Denmark||IM = Isle of Man||NO = Norway||VA = Vatican City
|-
|E6 = England (see also G7, UK)||IN = India||O8 = Ottoman Empire||W3 VA = WalesVatican City
|-
|EE = Estonia||IS = Iceland||OM = Oman||W3 = Wales
|-
|EG = Egypt
|}
Many locations have been part of different countries over the centuries. Items are shelved by the name of the ruling country at the time in questioncovered by the item. When works cover a long period, they are shelved under the current most recent name, or rarely occasionally under the most common one.
This is a particular challenge for what's now the United Kingdom. While there's a tendency in genealogy to use UK for all areas now included in the country, this is not the case in the field of history. There are many works that pertain only to Scotland, Wales, Ireland, or Northern Ireland. These works are shelved under those names as a means of subdividing the UK. A very few works address only the period when the name of the country was England or Great Britain, and those are shelved there.
====State Classifications====
|-
|C4 = Celts
|-
|F7 = Franks
|-
|M6 = Moors
|-
|N3 = Native Americans
|}
Other classifications that have been proposed, but not yet implemented, are: {| class="wikitable" style="text-align: left"|-|F7 = Franks|-|M6 = Moors|}will be created at need.
==Second Line==
===Date Code===
Classification RB is organized by the date of birth of the biographee. When the subject is a couple, the birth date of the senior is used (as Victoria for Victoria & Albert). This avoids the challenges created by monarchs who ruled multiple countries, variations in the spelling of names, and the inadequacy of House names for identification. It has the benefit of shelving contemporaries near one another. Birth dates can be difficult to find, especially in antiquity, but they permit the shelving of living monarchs and heirs, which death dates would not, and nor would coronation dates, which not all achieve. When dates are uncertain, the date given by [https://en.wikipedia.org/wiki/Main_Page Wikipedia] is normally used. Approximate dates are follwed by "c"for circa, as: "1069c".
Dates BC are preceded with those initials, and all dates are padded to four digits. Thus:
It has not yet been found necessary to add the day, but at need that would be added in the same way as the month. Beyond that, we'll have to think on it. So far, twins have all been dealt with in the same volume.
==Third Line==