I'm using jQuery validate plugin. I have 3 fields, and need to validate them only if one of them is not empty, otherwise do not validate at all.
<input type="text" data-validate="{validate:{required:true,
messages:{required:'Flickr set is required'}}}" id="flickr_set" name="flickr_set">
<input type="text" data-validate="{validate:{required:true,
messages:{required:'Flickr ID is required'}}}" id="flickr_id" name="flickr_id">
<input type="text" data-validate="{validate:{required:true,
positiveNumber:true, messages:{required:'Photos count is required',
positiveNumber:'Positive number is required'}}}" id="flickr_photos-count" name="flickr_photos-count">