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/// @startDocuBlock databaseDropDatabase
/// @brief drop an existing database
/// `db._dropDatabase(name)`
///
/// Drops the database specified by *name*. The database specified by
/// *name* must exist.
///
/// **Note**: Dropping databases is only possible from within the *_system*
/// database. The *_system* database itself cannot be dropped.
///
/// Databases are dropped asynchronously, and will be physically removed if
/// all clients have disconnected and references have been garbage-collected.
/// @endDocuBlock
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