Active mask

The Object Id of the Data or Alarm Mask that is displayed as soon as the Working Set is active (or visible, if the VT supports multiple Working Sets on the screen at the same time). For Working Sets compatible with VT version 6 and later, this value must reference a valid mask even if it is not selectable.

For Working Sets compatible with VT version 5 and earlier, and if the “selectable” attribute has the value 0, this attribute is ignored (no range validation).

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