`query`: plain words (e.g. "unemployment rate", "median home price").
Returns series IDs with title, units, native frequency, and a
`copyrighted` flag — some FRED series are owned by third parties whose
terms (in the series notes) apply beyond personal use. Resolve a series
ID here first; the data tools key off it.

`series_id`: a FRED series ID (e.g. "GDPC1"). The `notes` are returned
verbatim — they carry methodology caveats and, for third-party series,
the owner's copyright terms (also flagged via `copyrighted`).

`series_id`: a FRED series ID. `start`/`end`: ISO dates bounding the
window. `transform`: level | change | pct_change | pct_change_yoy | log.
`frequency`: optionally downsample to daily/weekly/monthly/quarterly/
semiannual/annual (with `aggregation` avg | sum | eop); only coarser than
the native frequency is valid. `max_points` caps the result, keeping the
most RECENT points (`truncated` tells you when the cap bit).

Values are CURRENT (post-revision) data. For numbers as originally
published, use `get_series_as_of` / `get_revision_history`.

`series_id`: a FRED series ID. The value is the most recent NON-MISSING
print (daily series publish '.' on holidays) and is CURRENT data — it may
itself be revised later (see `get_revision_history` for how much this
series typically moves). `next_release_date` is null when FRED publishes
no schedule for the series' release.

`series_ids`: 2-5 FRED series IDs. Same `start`/`end`/`transform` as
`get_observations`. If the series have DIFFERENT native frequencies you
must pass `frequency` (a frequency at least as coarse as the coarsest
series) — mixing frequencies without it returns misaligned dates. Units
differ per series unless a relative transform (e.g. pct_change_yoy) is
used — check each entry's `units` before comparing levels.

`days`: how far ahead to look (1-90, default 14). Returns each release's
name and date, soonest first. Dates are the SCHEDULED dates FRED knows
about; not every release publishes a schedule.

`series_id`: a FRED series ID. `as_of`: the knowledge date (ISO) — e.g.
"2009-03-18" shows the data the Fed saw at its March 2009 meeting.
`start`/`end` bound the observation window as usual.

Vintage coverage varies by series: dates before the first vintage have no
data (check `get_vintage_dates`). Values can differ sharply from today's —
that's the point.

`series_id`: a FRED series ID. `observation_date`: the data point's PERIOD
START date (ISO) — quarterly series use quarter starts (Q4 2008 =
"2008-10-01"), monthly use month starts. Returns the earliest archived
value, every revision with its publication date, the current value, and
the total drift.

Caveat: ALFRED's archive starts late for many series (`archive_starts`
shows where). `initial_value` is the true first print — what
decision-makers actually saw — only when the archive reaches back to the
observation's original release.

`series_id`: a FRED series ID. Answers "how often is this revised?" and
bounds the vintage tools: `get_series_as_of` has no data before
`first_vintage`. The full list is capped to the most recent dates;
`total_vintages` is the true count.