Generally, do <i>not</i> hijack user experiences.<p>Scrolling, highlight&#x2F;selection colour, fixed-position elements (I&#x27;ve ended up nuking your site&#x27;s header entirely), autoplay audio&#x2F;video, mouse action, click actions (either opening left-click in new tab, or center click in same tab), etc.<p>All violate the principle of least surprise&#x2F;astonishment. Quite annoying.