checkbox formula

I am writing a survey with very complex branching. I'm new to this
technology.  
Could someone please explain how to use the formula field to show a text box
if *any* checkboxes have been selected? I've tried this (below) but the
result is if 1 is selected the text box shows. However, if 1 and 2 are both
selected the text field does not show. If you have reference material for
xpath form fields, I'd be forever grateful.

$question-1='1' or $question-1='2' or $question-1='3' or $question-1='4'

Thank you,
Yvonne

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