Enum FieldRule 

pub enum FieldRule {
    MinLength(usize),
    MaxLength(usize),
    Pattern(String),
    Email,
    Min(f64),
    Max(f64),
    NotEmpty,
    Custom(String, Box<dyn Fn(&Value) -> Result<(), String> + Send + Sync>),
}

A field validation rule.

Variants

MinLength(usize)

Minimum string length.

MaxLength(usize)

Maximum string length.

Pattern(String)

Must match regex pattern (simple contains check).

Email

Must be a valid email (contains @ and .).

Min(f64)

Numeric minimum.

Max(f64)

Numeric maximum.

NotEmpty

Must not be empty string.

Custom(String, Box<dyn Fn(&Value) -> Result<(), String> + Send + Sync>)

Custom validation function.