The form rule to append the selected allergy to the list of allergies in the multiline textbox does two things—it appends the single new allergy text to the existing text in the Known Allergies control, and at the same time it unchecks itself. In this way, the checkbox behaves as a button that responds when checked and then resets itself.
The full text of the formula to append the allergy to the existing allergies is as follows:
[Form].[Known Allergies]+[Form].[varCRLF]+[Form].[Allergy]
Notice that a line-feed variable is used to separate the previous entries from the new one. The variable is defined in the form variables tab as the string “\n” which is the escape character for a line feed.