The default irrelevance mode removes a field from the layout entirely — its row is hidden and its controls are disabled.
data-fs-irrelevant="disabled" keeps a field in the layout but dims it instead of hiding it — for when seeing the field carries information. Here the dimmed shipping address mirrors billing as you type, showing exactly what will be used; uncheck to edit it independently.
data-fs-irrelevant="disabled"
valid(account-password) keeps the confirm field disabled until the password is answered and valid, and data-fs-clear-on-change wipes a stale confirmation whenever the password changes.
valid(account-password)
data-fs-clear-on-change
One expression models the whole rule: a work trip always needs a visa; otherwise only non-citizens staying past 90 days do. Parentheses, ||, &&, and a numeric comparison across three fields of three control types.
||
&&
data-fs-relevant on a container governs every field inside it with one expression; on an element holding no fields at all, it simply shows and hides content.
data-fs-relevant
Nothing to fill in now — we will email an invoice after checkout.
data-fs-relevant on one member of a choice group governs that member alone. The group reads its relevant members only. A checked member that goes irrelevant stops counting, and it counts again when its condition returns.
An option takes the attribute too. The engine removes an irrelevant option from its list and puts it back in document order when it returns. In disabled mode, two members of one set can exclude each other.
option