require at least one checkbox?
I have a form with a group of checkboxes where the user must select at least one, but can select more than one in any combination. I have no idea how to set up validation to require at least one of them. Below is the form code I'm using. Thanks!
<div class="lineGroup">
<label class="checklabel" for="study_print"><input type="checkbox" name="study_print" id="study_print" value="yes" class="formCheckboxField_Standard" <?php if (!(strcmp((isset($_GET["invalid"])?ValidatedField("rrf2017insert2","study_print"):""),"yes"))) {echo "checked=\"checked\"";} ?> tabindex="27" title="Please enter a value."> Print</label>
<label class="checklabel" for="study_digital"><input type="checkbox" name="study_digital" id="study_digital" value="yes" class="formCheckboxField_Standard" <?php if (!(strcmp((isset($_GET["invalid"])?ValidatedField("rrf2017insert2","study_digital"):""),"yes"))) {echo "checked=\"checked\"";} ?> tabindex="27" title="Please enter a value.">Digital</label>
<label class="checklabel" for="study_combined"><input type="checkbox" name="study_combined" id="study_combined" value="yes" class="formCheckboxField_Standard" <?php if (!(strcmp((isset($_GET["invalid"])?ValidatedField("rrf2017insert2","study_combined"):""),"yes"))) {echo "checked=\"checked\"";} ?> tabindex="27" title="Please enter a value.">Print + Digital</label>
</div>