code: function msgBox(messageHTML) {
          var msgEl = document.querySelector('.msg-box'),
              rect = this.getBoundingClientRect();
  
          msgEl.style.top = window.scrollY + rect.bottom + 8 + 'px';
          msgEl.style.left = window.scrollX + rect.left + 8 + 'px';
  
          msgEl.style.display = 'block';
  
          msgEl.querySelector('.msg-box-close').addEventListener('click', closeMsgBox);
          msgEl.querySelector('.msg-box-content').innerHTML = messageHTML;
  
          this.classList.add('filter-box-warn');
      }
docs: Display an error message box.
  @this {Element} The offending input field.
  @param {string} messageHTML