Look Back Blocking (Ext. Attr.)


Look Back Blocking eliminates decisions where the specified standard or extended attribute in the tail item of the destination region match the corresponding attribute in one or more items following the head item of the source region.


This function block has the following parameters:



Always Evaluate

Hard, Soft or Breakable.

Controls what happens when the extension eliminates all items in the range source.



All items will remain eliminated. Enter a wait state after the logic script has completed.



Roll back any eliminations made by this extension.



Roll back any eliminations made by this extension that have a danger point value of TRUE (non zero).

Routing modules will first use the danger defined for each individual decision.

However, one of the following may occur instead.







No danger point has been configured for the decision.

The site-wide danger point will be used.



This function block is used in the decision output logic.

The site-wide danger point will be used.



No danger point can be found for a decision.

The decision remains eliminated.

Region Id

Region to search. If blank, each decision's source region will be searched.

Last Location

Number of locations to look back.

Item Class Class of item to compare.

Item Class

Class of the item.


Name of the standard or extended attribute to compare.

Attribute Start Byte

Starting character within the standard or extended attribute.

Attribute Length

Specifies the number of characters in the attribute to compare.

Enter zero in both the Start Character and Attribute Length fields to use all characters.

Note: All the function blocks that deal with extended attributes can be provided INTERNALHOLD text to read the value of an internal hold.

Values are:


Internal Hold is not set.


Internal Hold is set.

However, you cannot use any of the extended attribute function blocks to modify system attributes.

More information

Look Back Blocking example.

Look Back Blocking pseudo code.

Routing function blocks list.