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A sheet of stamps is the original form in which they were
manufactured, typically consisting of an array of one of more stamps
(possibly of different types), plus a margin that may have its own
design and textual inscriptions. A block is a part
of a sheet that consists of one or more stamps in a contiguous group.
Nearly all types of stamps have an associated sheet type. In the se-tenant case, several stamp types will share a single sheet type.
Souvenir sheets, miniature sheets, and booklet panes are all special cases of sheets.
Most properties of a sheet are inherited from the stamps on the sheet, such as issuer, issue, watermark, gum, etc.
Layout describes how the different types of stamps and/or labels are arranged within the sheet.
For many modern stamps, what is sold as a "sheet" of stamps is actually a pane cut from a larger "press sheet", and some postal administrations have sold uncut press sheets in addition to regular sheets. We may add the distinction in future.