// Package validate provides small, composable value validators.
//
// A validator is just a func(T) error: it returns nil when the value is
// acceptable, or an error describing the problem. Nothing has to implement
// an interface, so a plain closure works anywhere a validator is expected.
// Combine validators with [All] (stop at the first failure) or [Collect]
// (run them all and join every failure).
//
//	username := validate.All(
//		validate.MinLength(3),
//		validate.MaxLength(16),
//		validate.Chars("abcdefghijklmnopqrstuvwxyz0123456789_"),
//	)
//	if err := username(input); err != nil {
//		// errors.Is(err, validate.ErrDisallowedChars) still works here
//	}
//
// Errors are plain sentinel values (see [Error]); match them with
// errors.Is. [Err] matches any error produced by this package.
//
// # Comparison with other packages
//
//   - go-playground/validator drives validation from struct tags and
//     reflection.
//   - go-ozzo/ozzo-validation composes rules in code, but through a Rule
//     interface over interface{}.
//   - asaskevich/govalidator is a bag of IsX string helpers.
//
// This package is the code-composition style with two constraints kept
// deliberately: validators are ordinary generic functions, checked by the
// compiler with no reflection ([In], [Equal] and the rest will not accept
// the wrong type), and there are no dependencies outside the standard
// library.
//
// # When to use something else
//
// Reach for go-playground/validator if you want struct-tag validation,
// translated messages, or a large catalogue of built-in checks. This
// package stays small and leaves struct/field wiring and error
// presentation to the caller.
package validate