Required conditional abilities are ones that do not use the word "may". When a required conditional ability's triggered condition is met, it is required to be triggered. The opposite of a required conditional ability is an optional conditional ability.

Page 21, Column 2, Paragraph(s) 2, Core Rule Book
If a conditional ability does not use the word "may" in its description, it is a required conditional ability. It must be triggered when its trigger condition is met, although the exact time of resolution may vary.
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