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The «button» macro should be provided with a link in a string:
<<button "[[displayed text|passage name]]">>
For instance, if the macro
«textinput $FoodName» appears in the same passage with a «button», and the text “pretzels” has been entered into the input box, then clicking the button will, in addition to changing passages, run the equivalent of
«set $FoodName to “pretzels”».