html - <main> inside <article> in HTML5 -

plot: when building coupons website realize can content not unique page should used inside <main><article> ..here..</article></main>.

problem: because w3schools state :

the content inside element should unique document. should not contain content repeated across documents.

but have content inside article. every time example a coupon can used entering code deal can activated going landing page. repeated in every 'coupon' post publish. tried use was.

<main><article><main>unique content</main> <aside>a coupon can used entering code deal can activated going landing page</aside></article></main> 

but again :

 note: there must not more 1 <main> element in document.  <main> element must not descendent of <article>, <aside>,  <footer>, <header>, or <nav> element. 

so best way format un-unique content inside <main> and/or <article>.

the main tag should used group article , aside elements.

<main>     <article>         unique document content.     </article>     <aside>         related content document.     </aside> </main>