“Below the fold” means content outside the initial visible viewport that a person reaches by scrolling. It is still part of the page. This differs from a collapsed panel, a hidden element or content that has not yet loaded.
Give the page a readable order
Put the topic and orientation first, then the explanations and examples that need more room. Use meaningful headings so a reader can scan or navigate directly to a section. A contents list can help a long lesson without forcing everything into the first screen.
Test where the boundary falls
Viewport height, width, browser chrome and zoom change what is initially visible. A paragraph may be below the boundary on one device and above it on another. Do not write content rules around a single screenshot’s exact position.
Exercise: open a long lesson, resize its window and zoom to 200%. Check that the next section follows naturally and that no fixed overlay blocks it. Try a section link to confirm that scrolling reaches the intended heading.
Load deliberately
Lazy loading can save work for nonessential images and previews, but the core explanation and navigation should remain readable. Avoid an empty placeholder that gives no clue what is coming.
Compare above the fold, headings and overflow. Normal scrolling is a layout behavior, not proof that someone has engaged with the content.
Sources
Reference 1 Reference 2 provide the technical details and current compatibility information.