Tim,
We mimic the Informix 4gl attribute so this will certainly never change.
From Informix 4gl doc:
INVISIBLE
The INVISIBLE attribute prevents user-entered data from being echoed on the
screen during a CONSTRUCT, INPUT, INPUT ARRAY, or PROMPT statement.
Usage
Characters that the user enters in a field with this attribute are not displayed
during data entry, but the cursor moves through the field as the user types.
Seb