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/// @startDocuBlock executeTransaction
/// @brief executes a transaction
/// `db._executeTransaction(object)`
///
/// Executes a server-side transaction, as specified by *object*.
///
/// *object* must have the following attributes:
/// - *collections*: a sub-object that defines which collections will be
///   used in the transaction. *collections* can have these attributes:
///   - *read*: a single collection or a list of collections that will be
///     used in the transaction in read-only mode
///   - *write*: a single collection or a list of collections that will be
///     used in the transaction in write or read mode.
/// - *action*: a Javascript function or a string with Javascript code
///   containing all the instructions to be executed inside the transaction.
///   If the code runs through successfully, the transaction will be committed
///   at the end. If the code throws an exception, the transaction will be
///   rolled back and all database operations will be rolled back.
///
/// Additionally, *object* can have the following optional attributes:
/// - *waitForSync*: boolean flag indicating whether the transaction
///   is forced to be synchronous.
/// - *lockTimeout*: a numeric value that can be used to set a timeout for
///   waiting on collection locks. If not specified, a default value will be
///   used. Setting *lockTimeout* to *0* will make ArangoDB not time
///   out waiting for a lock.
/// - *params*: optional arguments passed to the function specified in
///   *action*.
///
/// @endDocuBlock
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