Changes in version 0.1.2                        

  - New steps: require_scalar(), require_not_null(), require_unique(),
    require_named().
  - New steps: require_positive() and require_negative() with strict
    argument (non-strict by default).
  - require_integer() gains a strict argument. Default (strict = FALSE)
    accepts any numeric whole number; strict = TRUE requires the R
    integer type.

                        Changes in version 0.1.1                        

  - Export fail() so custom steps produce canonical structured errors.
  - as_contract_text() now capitalizes every sentence, not just the
    first.
  - require_between() and require_one_of() omit the At: line for scalar
    values where it adds no information.
  - Vignette: added "Data Frame with Mixed Constraints" section,
    surfaced immutability in the overview, updated custom step examples
    to use fail().
  - README: tightened prose, removed AI-ish phrasing.

                 Changes in version 0.1.0 (2026-03-09)                  

  - Initial release.
  - Core constructor: restrict() for building composable validators.
  - Building blocks: require_df(), require_numeric(),
    require_character(), require_length(), require_length_matches(),
    require_nrow_min(), require_has_cols(), require_col_numeric(),
    require_col_character(), require_col_range(), require_range(),
    require_one_of().
  - Dependent validation via one-sided formulas with explicit context
    passing.
  - Path-aware error messages (e.g. newdata$x2 must be numeric).
  - as_contract_text() for roxygen-compatible documentation.