func (rule *RuleLowercase) Validate(value string) (bool, error) {
	for _, c := range value {
		if unicode.IsLetter(c) && !unicode.IsLower(c) {
			return false, nil
		}
	}
	return true, nil
}
Validate checks if every letter is lower
package main
import (
	"sync"
	"unicode"
)
type RuleLowercase struct {
	Name string
	*sync.RWMutex
}
func (rule *RuleLowercase) Init() Rule {
	rule.Name = "lowercase"
	rule.RWMutex = new(sync.RWMutex)
	return rule
}
func (rule *RuleLowercase) GetName() string {
	rule.Lock()
	defer rule.Unlock()
	return rule.Name
}
func (rule *RuleLowercase) SetParameters(params []string) error {
	return nil
}