Change top level requirement wording (#7336)
Change top level requirement wording (#7336)

Changed the wording to be more consistent between `<svelte:window>`, `<svelte:body>` and `<svelte:head>`.
Chose "may only appear" over "has to appear" as the latter could be misinterpreted as a compulsory element
sveltejs/svelte,sveltejs/svelte