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Boxed collections are housed in two different ways. Either they are in acid-free file folders with a reinforced tab that stand upright inside legal-sized flip-top document boxes, or they are in 2-flap acid-free folders without any tab that rest flat in a box with an attached lid (called a clam-shell box) or removable lid box ) that was specially designed for ease of use in the Reading Room(which is slightly shorter). Usually collections that present few special housing considerations and are not frequently used are stored upright and sent to HD. If a collection is too fragile to go to HD, or if heavy use is expected, it may instead be kept in flat boxes on site, since Houghton shelving is adjusted to accept flat boxes about 4" high. Shelving in the Harvard Theatre Collection (HTC) and at HD can accept either upright or flat boxes. When a collection uses both flat and upright boxes, each type has an identifying prefix. Manuscripts in the standard-size box, whether flat or upright, have the prefix "bMS", meaning "boxed manuscript", as part of their call number. Any flat boxes larger than the standard size are called "pfMSpf" boxes, for "portfolio manuscript"(portfolio) boxes. Rarely, an upright box that is part of a larger collection must be kept at Houghton, and in that case it has no prefix, and is shelved with upright bound volumes, as simply "MS", since it is too tall for the regular boxed manuscript shelves. This was reviewed in more detail under the previous section: "Call numbers/accession numbers, housing /storage indicators, shelving categories, and special locations".
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