Solution
A implicitly linked
property node or
invoke node is created from the front panel object or block diagram terminal by right-clicking them and selecting
Create>>Property Node from shortcut menu. The image below is a property node implicitly linked to a string control. As they are implicitly linked, they have the same label name.
An explicitly linked property node or invoke node is a generic property node or invoke node that requires a front panel object or block diagram terminal reference wired to its reference input terminal. The image below is an explicitly linked property node example.
You must use explicitly linked property nodes or invoke nodes if they will be part of a subVI.