支持了window当然也不能忘了document不是，毕竟有些事件还非得在document上触发, 比如: selectionchange .
来使用<svelte:document>给document对象添加上onselectionchange事件处理函数:

The <svelte:document> element allows you to listen for events that fire on document. This is useful with events like selectionchange, which doesn’t fire on window. Add the onselectionchange handler to the <svelte:document> tag:

<svelte:document {onselectionchange} />

偷偷告诉尽量避免在document元素上使用mouseenter和mouseleave哦，因为有些浏览器不支持，可以用在<svelte:body>上. 这都是技巧

Avoid mouseenter and mouseleave handlers on this element, as these events are not fired on document in all browsers. Use <svelte:body> instead.