Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 16)

Chapter 1 Designing Add-On Instructions
Parameters
The parameters define the instruction interface; that is, how the instruction
appears when used. The parameter order defines the order that the parameters
appear on the instruction call.
Local tags
The Local Tags tab defines tags that are used by the logic within the Add-On
Instruction and are not visible outside the instruction. Other Add-On
Instructions or programs in the project cannot access these tags.
The only way to make a local tag or one of its members accessible from outside the
instruction is by defining an alias parameter.
16 Rockwell Automation Publication 1756-PM010F-EN-P - October 2014