code: func MinLength(val int) {
  	if a, ok := attributeDefinition(); ok {
  		if a.Type != nil && a.Type.Kind() != design.StringKind && a.Type.Kind() != design.ArrayKind && a.Type.Kind() != design.HashKind {
  			incompatibleAttributeType("minimum length", a.Type.Name(), "a string or an array")
  		} else {
  			if a.Validation == nil {
  				a.Validation = &dslengine.ValidationDefinition{}
  			}
  			a.Validation.MinLength = &val
  		}
  	}
  }
docs: // MinLength can be used in: Attribute, Header, Param, HashOf, ArrayOf
  //
  // MinLength adds a "minItems" validation to the attribute.
  // See http://json-schema.org/latest/json-schema-validation.html#anchor45.