Most notably the pages have no <title> tag which means browsers don't show a title at all which makes it difficult to distinguish between pages when multiple documentation tabs are open.

Additionally search indexes guess at the title for search results which usually goes well

But sometimes it does not

Adding a <meta name="description" content="Page description here." /> can also help to provide a short description of the page which helps users in search results find what they're looking for more quickly (for those not using the on-site search).