Anything sampled per page and able to report how long it lasts.
A track, a sequence, and a group built here all satisfy it, which is what lets groups nest and lets a member be swapped for a sequence without the call site changing.
track
sequence
Readonly
How long one pass takes, in seconds.
The value at one page. index overrides the page's own position when sampling a group.
index
Optional
How long count pages take in total, in seconds — a pass plus whatever stagger separates them.
count
Anything sampled per page and able to report how long it lasts.
A
track, asequence, and a group built here all satisfy it, which is what lets groups nest and lets a member be swapped for a sequence without the call site changing.