I suppose it would depend on the evaluation. The SPLIT function could be used to break the text up based on line breaks, but I don't know if that would really lead to anything useful for this.

Since multi line fields don't have regex, I'd say your best option is a custom validator.

   window.Parsley.addValidator('multilineformat', {
    validateString: function(value, requirement, field) {
      var valid = true; // default validation output
      
      // loop values split on line break
      // may need adjustment for other possibilities like carriage returns
      $.each(value.split('\n'),function(index, value){
        // add your evaluation here and return false if not valid
        if (value == 'test') {
          valid = false; // set validation to false if any line fails
        }
      });
      
      return valid;
    },
    messages: {
      en: 'Invalid format.', // whatever error message you want
    }
  });
  
  // assign validator to field
  $('.myMultiLine textarea').attr('data-parsley-multilineformat','');