# weightflow 1.2.0

## New features

* **Two-phase (double) sampling.** `step_subsample()` records a second phase of sampling (a subsample drawn for a costlier follow-up), and `bootstrap_weights()` then returns the two-phase variance `V = V1 + V2` -- the phase-1 sampling variance plus the phase-2 conditional variance a single-phase bootstrap would miss. Covers a Poisson second phase nested in the first; calibrating the subsample to first-phase totals (the two-phase regression estimator, Fuller 1998) is done by composing with a `reference_sample()`. **`two_phase_variance()`** splits the estimate's variance into its phase-1 and phase-2 components (`V1`, `V2`, and the share `V2/V`), turning the coupling into an operational read of whether a denser subsample would pay off. The HTML report now explains the subsample step (in English and Spanish) and its `V = V1 + V2` logic. Validated against Monte Carlo; see `vignette("two-phase-sampling")`.
* **Non-probability samples.** `weighting_spec(base_weights = NULL, nonprob = TRUE)` starts an opt-in / volunteer / river sample, and `step_pseudoweight()` estimates each unit's participation propensity against a `reference_sample()` and assigns the inverse-propensity pseudo-weight (Elliott and Valliant 2017). Can be combined with calibration to the reference for a doubly robust estimate.
* **`step_nr_sensitivity()` / `nr_sensitivity()`** add a sensitivity analysis for nonignorable nonresponse or selection (proxy pattern-mixture model, Andridge and Little 2011), reporting an *ignorance interval* over a single sensitivity parameter; the report gains a matching block.
* **`data_defect()`** brings the data-defect view of Meng (2018) to non-probability samples: the effective sample size across a grid of plausible outcome-participation correlations (an ignorance range, not a single number).
* **`write_recipe()` / `read_recipe()`** serialize the recipe (the method, not the data) to a human-readable, versionable YAML file and read it back into an inspectable manifest or an executable `weighting_spec`. Needs the `yaml` package.
* **`domain_summary(min_n_eff = )`** turns the per-domain reliability read into an explicit publication gate (a `publishable` column and a warning for domains below the threshold, pointing to `as_sae_input()`).
* **Confidentiality tools for public-use files.** `collect_replicate_weights(scramble = TRUE)` hides the sampling design behind the exported replicate weights (variance unchanged), and `disclosure_risk()` flags weight outliers within a publication cell.
* **`as_sae_input()`** exports, per domain, the direct estimate, its recipe-aware design SE, the effective sample size and a CV rating, in the shape a Fay-Herriot model consumes -- a bridge to the SAE packages (`emdi`, `sae`, `hbsae`) without fitting any model.
* **Calibrate to a reference survey.** `reference_sample()` lets `step_calibrate()` and `step_model_calibration()` calibrate to a weighted reference survey instead of a full population frame; passing its replicate weights propagates the reference's sampling variance through the bootstrap (Opsomer and Erciulescu 2021), and the report states when control totals are estimated rather than census figures.
* **`weighting_alerts()` / `has_alerts()`** read the quality incidents recorded by `prep()`; every incident now lands in `$alerts`, a single reliable channel for programmatic quality control even under suppressed warnings.
* **`bootstrap_weights(fpc = )`** adds a finite-population correction (column, scalar, or per-stratum vector) folded into the Rao-Wu rescaling (Rao, Wu and Yue 1992; Beaumont and Patak 2012); matters for the high sampling fractions common in LatAm household surveys. `fpc = 0` / `NULL` is the with-replacement bootstrap.
* **`t` and percentile confidence intervals** for `bootstrap_estimate()` (and `t` for `jackknife_estimate()`), carrying the design degrees of freedom so the interval is not anticonservative with few PSUs. Default stays `"normal"`.
* **Stable step ids.** Every `step_*()` gains an `id` (with a unique derived default), shown in the recipe print-out and usable to select a step in `collect_step_detail()`.

## Bug fixes

* Nonresponse, eligibility and weight-trimming steps now build their `by`-cells over the units still active, so cases dropped earlier in the cascade no longer raise spurious `(missing)`-cell warnings; the response-rate card likewise ignores out-of-scope cases with a missing disposition rather than counting them as nonresponse.
* Household-level nonresponse modelling now reports the same tiny-propensity and calibration diagnostics as the person-level path.
* **Behaviour change:** the mean estimators and replicate-weight exports keep active negative weights (a valid GREG output) rather than dropping them, matching the totals estimators and the survey exports; estimates and standard errors may shift accordingly.
* Stricter, earlier argument validation across the step constructors and estimators, with clearer messages (out-of-range or non-numeric arguments, duplicated calibration-total names, negative model weights, blank stratum/PSU ids) instead of later cryptic errors.
* Assorted robustness fixes for malformed or edge-case inputs (missing calibration auxiliaries, empty or degenerate cells, open trimming bounds), each covered by a regression test.
* Report accuracy and honesty fixes: no vacuous checklist claims, clearer per-step descriptions, and formatting/translation fixes.
* Documentation: an argument-correspondence table (`?weightflow-concepts`), a quality-alerts catalogue (`?weightflow-alerts`), and `@family` cross-links.

# weightflow 1.1.0

## New features

* **Diagnostics report suite.** `report_weighting()` gains a per-step card reading the bias-variance trade-off of each adjustment, with quality alerts for trimming, calibration, machine-learning propensity models and nonresponse-by-calibration.
* **Honest variance for machine-learning adjustments.** A flexible learner (tree / forest / boost) run without `crossfit` now raises an alert, since same-sample predictions can understate the variance even under recipe-aware replication; the `ranger` seed is fixed so the forest's noise no longer enters the replicates.
* **`collect_replicate_weights()` also exports delete-a-PSU jackknife objects**, with the `type` / `scale` / `rscales` needed by `survey` / `srvyr` (first argument renamed `boot` -> `object`).
* **Iterative recipe refinement.** Adding a step to a prepped recipe clears the results with a message and re-runs the cascade on the next `prep()`, so stale weights cannot be read by accident.
* **Per-subgroup trimming.** `step_trim_calibrated()` gains a `by` argument and per-group `lower` / `upper` bounds (requested by ECLAC).
* **`collect_propensities()`** recovers the per-unit response propensities fitted by a `step_nonresponse(method = "propensity")` step from a prepped recipe, so their distribution can be inspected before the adjusted weights are trusted; it returns the same information whether the adjustment was made at the unit level or, through `cluster`, at the household level (the household propensity is broadcast to its members). It also returns `.factor` (the multiplier actually applied to each unit) and, with propensity classes, `.class`; note that `1/.propensity` reconstructs the applied factor only when `num_classes = NULL`. Requested by ECLAC.
* **`collect_step_detail()`** is a generic companion to `collect_weights()`: for any step it returns the weight each unit received (`.weight_in`) and the multiplier the step applied (`.factor`, read from the stored stage weights so `.weight_in * .factor` equals the outgoing weight by construction), plus that step's native per-unit quantities when it exposes them (for a propensity step, `.propensity` and `.class`).
* **`domain_summary()`** reports, for a study domain (e.g. a department / DAM), how the weights move within each domain at every stage of the cascade -- active units, sum of weights, mean weight and Kish design effect -- so weight movement can be reviewed step by step per domain for quality control (requested by ECLAC). Domains follow their factor / numeric order, a missing domain value is shown as an explicit `(missing)` domain, and `by` accepts several columns (crossed).

## Bug fixes and documentation

* Robustness and correctness fixes for uncommon edge cases -- malformed or degenerate inputs, replicate-variance accounting, and the HTML report -- each covered by a regression test.
* Documentation overhaul: help pages reviewed and rewritten, estimator formulas added to the details, and a new `?weightflow-concepts` page.

# weightflow 1.0.0

## New features

* **Tidy control totals that disagree on N now reconcile instead of failing.**
  When the tidy `totals` given to `step_calibrate()` do not all sum to the same
  population size (typical rounding of independently produced control totals),
  the largest margin is kept as the reference N and the others are rescaled
  proportionally, so their internal distribution is preserved and the
  calibration always closes. This applies to both `method = "raking"` (which
  previously could fail to converge) and `method = "linear"` / GREG (which
  previously used the first margin silently). The adjustment is reported through
  a message (informative, never fatal, so it is safe under
  `options(warn = 2)`) and is carried into `report_weighting()`, where it appears
  in the points-of-attention panel and the calibration step card listing every
  rescaled margin and the common N, so control-total mismatches are surfaced for
  review rather than hidden. This keeps the tidy interface usable without the
  manual dropping of a category that a design matrix would otherwise require.

* **Unweighted propensity models.** `step_nonresponse(method = "propensity")`
  gains `weight_model` (default `TRUE`). With `FALSE` the response-propensity
  model is fit unweighted, so the incoming weights enter only the 1/p (or class)
  adjustment and not the model fit -- useful when the weights are unrelated to
  response given the covariates (Little & Vartivarian 2003). Works at unit and
  household (cluster) level and across all engines. On a suggestion by Andrés Gutiérrez (ECLAC - Statistics Division).

* **Nonresponse by calibration (two-phase).** `step_nonresponse()` gains
  `method = "calibration"`: instead of weighting classes or inverse propensities,
  it adjusts for nonresponse by calibrating the respondents' weights to auxiliary
  totals (Lundstrom & Sarndal 1999; Sarndal & Lundstrom 2005). With
  `totals = NULL` (default) the targets are the R+NR design-weighted totals at that
  stage, so the calibrated respondent estimates reproduce the pre-nonresponse
  cascade estimates exactly (the two-phase / sample-level case, Estevao & Sarndal
  2002); supply `totals` to calibrate to population totals instead. Continuous and
  categorical auxiliaries, the distance `calfun` (linear/raking/logit), `bounds`
  and `penalty` (ridge) all carry over from `step_calibrate()`. The sample-level
  target is recomputed inside each bootstrap/jackknife replicate, so the two-phase
  variance is captured by the recipe-aware machinery. With
  `equal_within_cluster = TRUE` (and a `cluster`) the adjustment is integrative
  (Lemaitre-Dufour): the responding members of a household share a single
  calibration factor, so nonresponse calibration keeps the weights constant
  within household, as in a household survey. `method = "weighting_class"`
  remains the post-stratification (joint-cell) special case; the marginal
  (IPF via `margins`) variant is planned for a later 0.3.0 increment.

* **`step_trim_calibrated()`: trimmed (range-restricted) calibration.** Trims
  already-calibrated weights into an absolute interval `[lower, upper]` while
  **preserving the calibration totals**, unlike `step_trim_weights()` which caps
  and redistributes (breaking the constraints). It is a bounded re-calibration
  (the generalized exponential method of Folsom & Singh 2000): the targets to
  preserve are the totals the incoming weights already
  achieve, and the absolute-weight bound becomes a per-unit factor bound
  `w_new / w in [lower/w, upper/w]`, solved with the range-restricted Euclidean
  distance (`calfun = "linear"`, the default) or the multiplicative one
  (`"raking"`). Weights inside the range stay put; out-of-range ones saturate at
  their bound and the rest move minimally to restore every total. If the range
  is infeasible, the unmet totals are relaxed and a warning is raised. It reuses
  the bounded-calibration solver, now able to take per-unit bounds. With
  `equal_within_cluster = TRUE` (and a `cluster`) the trimming is integrative:
  one factor per household, so weights that were constant within household stay
  constant (the household-level analogue of `survey`'s `aggregate.stage`
  calibration).

* **Lonely-PSU handling and parallelism in the replicate-variance functions.**
  `bootstrap_weights()` and `jackknife_weights()` gain a `lonely_psu` argument:
  `"certainty"` (default) keeps the previous behaviour (single-PSU strata are
  self-representing, contribute no variance, and warn), while `"collapse"` merges
  single-PSU strata into a pseudo-stratum so they are resampled and yield a
  (conservative) variance instead of zero. Both functions also gain a `cores`
  argument: with `cores > 1` the per-replicate re-preps run in parallel via
  `parallel::mclapply` (forking; serial on Windows). The resampling is drawn up
  front from the `seed`, so the parallel run is bit-identical to the serial one.

* **`redistribute` argument for `step_trim_weights()`.** The trimmed mass can now
  be shared among the untrimmed units either in proportion to their weights
  (`"proportional"`, the default, keeps their relative sizes) or in equal amounts
  (`"uniform"`, the same amount to each untrimmed unit, with already-trimmed cases
  not reused). The `"uniform"` option reproduces `survey::trimWeights()` exactly,
  for bit-for-bit agreement when a weighting pipeline is validated against
  `survey`.

* **`report_weighting()` is now a full methodological quality report (GSBPM 5.6
  / ESS style).** With `narrative = TRUE` (default) the HTML report reads like an
  official quality report: an auto-generated executive summary (the cascade in
  prose plus the headline design effect, effective n and R-indicator) and a
  natural-language paragraph on each step built from its own parameters and
  diagnostics, in English or Spanish (new `lang`). A new `metadata` argument adds
  a reference-metadata header card aligned to the ESS SIMS / ESMS concepts and
  GSBPM sub-process 5.6 (operation, reference period, coverage, producer,
  contact, sampling frame, the source and date of the control totals, version,
  confidentiality). When the recipe has eligibility / nonresponse steps, a
  "Fieldwork outcomes" card reconstructs every case's disposition and reports the
  AAPOR response rate in three variants, from most to least conservative in how
  unknown-eligibility cases are treated, RR1 <= RR3 (CASRO, e-adjusted) <= RR5,
  weighted and unweighted (Valliant, Dever & Kreuter 2018, ch. 6). The executive
  summary also aggregates a "Points of attention" panel (steps that did not
  converge or raised an alert, each with a short recommendation), a truthful
  status checklist (convergence, final design effect, extreme and replicate
  weights, alerts) and a completion line; calibration steps get descriptive names
  by their auxiliaries and a relative-deviation column on their target/achieved
  tables. Set `narrative = FALSE` for the previous tables-only report.

* **New analytical cards, charts and navigation in `report_weighting()`.** A
  per-domain reliability card (new `domains` one-sided formula: active n, sum of
  weights, CV, Kish design effect and effective n within each domain, one table
  per term, `+` separate and `:` crossed). A per-step impact table (the change in
  Kish deff and CV versus the previous stage, each step's share of the total
  |deff change|, and whether it adds variance or recovers efficiency). A Kish
  design-effect evolution chart across stages. A replication-design card (new
  `replicates`, a `weightflow_boot` / `weightflow_jack` object: method,
  replicates, strata, mean PSUs per stratum, lonely-PSU handling, seed, cores and
  run time); `bootstrap_weights()` and `jackknife_weights()` now record this
  metadata. Plus a navigation menu, conditional colouring of the design-effect
  cells, a plain-language interpretation of the final design effect, collapsible
  per-step details, and a restyle to the package identity. Still pure inline SVG,
  no JavaScript and no new dependencies.

## Bug fixes

* **Cross-fitting no longer errors in a fresh session.** With a `crossfit_seed`,
  `step_nonresponse()` and `step_model_calibration()` saved and restored the
  global RNG state but assumed `.Random.seed` already existed, which fails in a
  session that has not yet drawn a random number (e.g. a vignette build). The
  state is now saved only when present and unset again otherwise.

* **`step_trim_weights()` now trims negative weights.** It previously acted only
  on positive weights (`w > 0`), so negative weights produced by unbounded linear
  calibration were left untouched by a lower floor. It now trims every non-zero
  weight, flooring negatives to `lower`, while still leaving dropped units (weight
  exactly 0) alone. Recipes without negative weights are unaffected.


* **Reproducible report scatter plots.** The weight before/after scatter in
  `report_weighting()` subsampled points at random (without a seed) when a step
  had more than 800 units, so the plotted cloud changed between renders even
  though the weights were identical. It now uses a deterministic thinning
  (`.thin_scatter()`): all points are drawn up to `cap = 3000`, and above that
  the plot always keeps both tails on each axis (smallest/largest weights before
  and after) and the largest departures from the y = x line, then systematically
  thins the dense core. The scatter is now identical across runs and never drops
  the outliers.

# weightflow 0.2.0

## New features

* **Tidy population totals for `step_calibrate()`.** In addition to the classic
  `margins`/`totals` inputs (which keep working unchanged), calibration targets
  can now be given as tidy data frames, paired with the new `count` argument
  that names the counts column:
    - *Post-stratification*: a data frame with one or more category columns plus
      a counts column. Several category columns are crossed automatically, so
      there is no need to build a collapsed cell variable by hand.
    - *Raking*: a list of data frames, one per margin.
    - *Linear/GREG*: a named list matching the formula terms, with a data frame
      (all categories) for each factor and a single number for each continuous
      total; weightflow builds the model.matrix totals internally, so the user
      never drops a reference category or handles the intercept.
  Calibration also reports clearer diagnostics and warnings: post-stratification
  flags cells in the sample but missing from the totals (error) or in the totals
  but absent from the sample (warning); raking warns on mutually inconsistent
  margins or non-convergence; linear calibration warns when the constraints are
  not fully satisfied; and calibration variables with missing values raise an
  informative error.
* **Subsampling of more than one person per household in `step_select_within()`.**
  A new `n_selected` argument (a single number or an unquoted column) works
  alongside `n_eligible` for simple random selection of a subsample: the weight is
  multiplied by `n_eligible / n_selected` (equivalent to
  `prob = n_selected/n_eligible`). It defaults to 1, so selecting a single person
  keeps working unchanged.
* **External consistency totals for `step_model_calibration()`.** The totals of
  the `x_formula` auxiliaries can now be supplied through the new `x_totals`
  argument, in the same two shapes as `step_calibrate(method = "linear")`: the
  tidy format (a named list with a data frame per factor, paired with `count`,
  and a single number per continuous total) or the classic model-matrix vector.
  This covers the common case where the X control totals come from an external
  source rather than from the frame; the auxiliaries then need to be present only
  in the sample, not in `population`. When `x_totals` is `NULL` (default) the X
  totals are still taken from `population`, so existing code is unchanged.
  `population` remains required, because the model-assisted block predicts each
  outcome over every population unit. Model calibration now also warns, like
  linear calibration, when the achieved totals do not fully satisfy the
  constraints (collinear or ill-conditioned auxiliaries).
* **Delete-a-PSU jackknife variance (recipe-aware).** `jackknife_weights()`
  builds jackknife replicate weights by deleting one PSU at a time and re-running
  the whole recipe on each replicate, so the replicate weights carry the
  variability of every adjustment. It is the stratified jackknife (JKn) with
  `strata`/`psu`, the unstratified jackknife (JK1) with `strata = NULL`, and the
  delete-one-unit jackknife with `psu = NULL`. `jackknife_estimate()` (plus
  `jack_total()` / `jack_mean()`) summarise a statistic with the JKn variance and
  match `survey`'s replicate jackknife for totals. `as_svrepdesign()` now also
  accepts a jackknife object, so the recipe-aware replicate weights flow into
  `survey`/`srvyr` for any estimand and any domain.
* **Domain (partitioned) calibration in `step_calibrate()`.** A new `by`
  argument names a domain (partition) column; the weights are then calibrated
  **independently within each domain**, each to its own totals (partitioned /
  domain calibration). The tidy totals carry the domain as a
  column, and a continuous total becomes a data frame `domain, value` (one total
  per domain); the domain variable does not go in the formula/margins. It
  composes with `calfun`, `bounds`, `penalty` and `equal_within_cluster`, applied
  within each domain, and reproduces every domain's benchmarks. `by = NULL`
  (default) calibrates globally, unchanged.
* **Exponential (raking) distance for `step_calibrate(method = "linear")`.**
  `calfun` now also accepts `"raking"` (the multiplicative distance g = exp(u)),
  next to `"linear"` and `"logit"`. It keeps the calibration weights positive
  without needing explicit `bounds` and still satisfies the constraints exactly,
  and works on mixed categorical and continuous auxiliaries as well as with the
  integrative option (`equal_within_cluster`, one weight per cluster). Matches
  `survey::calibrate(calfun = "raking")`.
* **R-indicator of response representativity (automatic diagnostic).** When the
  recipe includes a nonresponse adjustment, `summary()` and `report_weighting()`
  now report the R-indicator (Schouten, Cobben & Bethlehem), R = 1 - 2*S, with S
  the design-weighted standard deviation of the estimated response propensities
  over the eligible sample: closer to 1 means a more representative response and
  less nonresponse-bias risk. The report also shows the unconditional partial
  R-indicators by auxiliary, pointing to which variable drives the lack of
  representativity. It is computed on the auxiliaries of the nonresponse step and
  needs no new function or user action; recipes without a nonresponse step are
  unaffected.
* **Machine-learning response propensities** (CART, random forest and gradient
  boosting via `xgboost`) for `step_nonresponse()` and `step_model_calibration()`.
* **k-fold cross-fitting** (`crossfit`) to estimate each unit out-of-sample,
  with folds formed by cluster to avoid leakage.
* **Ridge (penalized) calibration** (`penalty`) to keep weights stable with many
  auxiliaries.
* **Potter MSE-optimal trimming** (`method = "potter"`), a data-driven cutoff.
* **Quality alerts in `prep()`.** `prep()` now computes non-fatal quality alerts
  and stores them on the prepped object (`$alerts`) and per step: negative or
  sub-1 weights and g-factors outside the Deville-Särndal bounds `[0.1, 10]`
  after calibration, small adjustment cells (new `min_cell_n`, default 30,
  following Kalton and Flores-Cervantes 2003) and excessive adjustment factors
  (new `max_factor`, default 2.5). Alerts always appear in the HTML report; set
  `prep(warn = TRUE)` to also raise them as R warnings.
* **Weight distribution and alerts in `report_weighting()`.** The report gains a
  "Weight distribution (final)" summary (min, p1, median, p99, max, max/min ratio,
  and counts of negative, sub-1 and extreme weights) and a per-step "Quality
  alerts" block.
* **New `disposition` column in the `sample_one` example data.** A single factor
  with the full field disposition (eligible respondent, eligible nonrespondent,
  household nonresponse, ineligible, unknown eligibility), recoded from the
  existing indicator columns (which are kept). It gives a tidy single-column view
  of the dispositions and can be used directly via logical conditions in the
  steps.
* **New vignette "Preparing the sample: eligibility and response before
  weighting"**, on how the input sample should be classified (the disposition
  tree), how it is sized (eligibility and response inflation) and how the
  dispositions map to the adjustment steps.

## Bug fixes

* The optional machine-learning engines (`engine = "forest"` via ranger,
  `engine = "boost"` via xgboost) now run single-threaded by default, for
  reproducibility and to respect the core limits applied in CRAN checks. Set
  `options(weightflow.num_threads = n)` to use `n` threads.

* `report_weighting()` now flags calibration steps that did not converge. When a
  raking, linear or bounded calibration stops without satisfying the requested
  totals (the same condition that already prints a console warning), the HTML
  report shows a "Did not converge" alert on that step and no longer states that
  the step converged. Previously the report always reported convergence,
  regardless of the actual result.

* `step_calibrate(equal_within_cluster = TRUE)` now implements the genuine
  Lemaitre-Dufour (1987) integrative method: each unit's auxiliaries are
  replaced by their household mean before a person-level calibration, so the
  per-household penalty scales with household size. This matches `survey`'s
  `calibrate(aggregate.stage = )` (Vanderhoeft 2001) to machine precision.
  The previous implementation used a household-level distance
  (summed auxiliaries, uniform per-household penalty), a different (non-standard)
  method. Integrative-calibration weights will change; totals are still met
  exactly and weights remain constant within household.

# weightflow 0.1.0

First release.

A dependency-free, pipeable API to compute survey weights from design base
weights through a chain of hierarchical adjustment stages. Build a recipe
lazily, estimate it with `prep()`, and extract the weights with
`collect_weights()`. Separating *define* from *apply* makes the whole process
reproducible and auditable, and lets the bootstrap re-run the entire cascade on
each replicate.

## Adjustment steps

* `step_unknown_eligibility()`: redistribute the weight of unknown-eligibility
  cases to the known ones (person- or household-level via `cluster`).
* `step_drop_ineligible()`: zero out out-of-scope units.
* `step_select_within()`: within-household selection (unequal `prob` or equal
  `n_eligible`).
* `step_nonresponse()`: weighting-class or propensity adjustment, at the person
  or household level (`cluster`).
* `step_calibrate()`: raking, post-stratification and linear/GREG calibration,
  with bounded (Deville-Särndal) and integrative (one weight per household)
  cluster options.
* `step_model_calibration()`: Wu-Sitter model calibration.
* `step_trim()`, `step_trim_weights()`, `step_round()`, `step_rescale()`:
  trimming, rounding and rescaling.
* `step_assert()`: quality checkpoint (deff, weight ratio, effective n).

## Inspection and reporting

* `summary()`, `plot()` and `weight_factors()` for per-stage diagnostics.
* `design_effect()` for the Kish design effect and effective sample size.
* `report_weighting()` builds a self-contained HTML report with a pipeline
  diagram, the variables used, per-stage summaries and per-step visuals.

## Variance estimation

* `bootstrap_weights()` resamples PSUs within strata (Rao-Wu rescaling) and
  re-applies the whole recipe on each replicate, so the replicate weights carry
  the variability of every adjustment.
* `boot_mean()` and `boot_total()` return the estimate, standard error and CI.
* `as_svydesign()`, `as_svrepdesign()` and `collect_replicate_weights()` bridge
  to the `survey` and `srvyr` packages for design-based inference.

## Data

* Bundled example datasets `population`, `sample_survey` (take-all roster) and
  `sample_one` (multistage select-one design), all with stratum, PSU and design
  weight.
