Collapsing hides content and also hides that the content exists
Aliases: accordion hiding · disclosure scent · collapsed section
What it is
An accordion puts a block of content behind a heading. The heading stays; the content leaves the layout. The cost is not only “one extra click to see it.” Once collapsed, the block’s existence is hidden with it: people stop counting it among what the page has. If the heading is vague (“More,” “Advanced”), even the category stops reminding anyone that options lived here. Collapse trades visibility for space, and what it spends is discoverability, not merely an extra click.
Why it happens
People build a page model from what is in front of them. Expanded, heading and content share an area, and the area itself says “there is something here.” Collapsed, the area shrinks to one heading line, and the model keeps only the label. The label must carry the whole existence claim, and it usually holds far less than the content — fees, exceptions, optional fields are not inferred from the words “Advanced settings.” People who never opened it treat it as absent; people who opened it and closed it also drop it from later decisions, because working memory is now computing on the collapsed page. Space was saved because existence was deleted from the model. That is different from putting content on another page: another page at least occupies a name in navigation. A collapsed block and its content share one heading; if the heading is weak, both sides are weak.
Studying it
Present the same fields always visible, collapsed by default, or expanded by default, and give people new to the product a task that requires a field inside the collapse. Record whether they open it, hesitation before opening, and later recall that “this block was on the page.” Independent variables: how specific the heading is, position on the page, presence of an incomplete mark. Dependent variables: discovery, omission, recall. Discovery should rise with a specific heading, which shows that existence is loaded onto the heading, not onto the widget’s shape.
Where it stops holding
When people already have a skill of “panels like this get opened” (a professional tool used daily), existence is patched by that skill and collapse mainly saves space. Content that must be seen for legal or safety reasons cannot be “saved” by collapsing; unseen is uninformed. On long mobile pages, collapsing secondary blocks trades existence for scroll cost and has to follow hit rate, not a blanket collapse. If a screen reader still walks collapsed nodes in the reading order, content that is visually “absent” is spoken, and the two page models diverge.
Applying it
- Collapse only truly secondary blocks whose heading can name the category; write the heading as a summary of the content, not “More.”
- If the block holds an unfilled required field or an error, leave evidence on the collapsed heading; do not let the error disappear with the content.
- Do not put decision-critical material (price breakdown, permission scope, irreversible consequences) in a default-collapsed block.
- How to check: show a collapsed screenshot to someone new to the page and ask them to list the functional regions. Any region they cannot name has already had its existence hidden.