Support for mutually exclusive groups of validations chained with OR

[adam-shamaa]

• [x] I have looked at the documentation here first?
• [x] I have looked at the examples provided that may showcase my question here?

Package version eg. v9, v10:

v10

Issue, Question or Enhancement:

I'd like to defined groups of validations from existing rules and chain them together with an OR clause. Something along the lines of

var req struct {
    Email string `binding:"(bakedin_tag1,bakedin_tag2)|bakedin_tag3"`
}

The syntax above of using parentheses/brackets isn't supported so I've tried defining an alias for the (bakedin_tag_1, bakedin_tag_2) clause:

validate.RegisterAlias("lcase_email", "email,lowercase")

However, there's a bug where aliases can't be used with an OR operator (existing issue for this https://github.com/go-playground/validator/issues/766)

Seem like the only route would be avoiding an alias and defining a custom validator function which validates the email and lowercase rule. But I want to avoid this as I'd be re-creating the baked-in validation methods isEmail and isLowerCase https://github.com/go-playground/validator/blob/a947377040f8ebaee09f20d09a745ec369396793/baked_in.go#L1675-L1678 https://github.com/go-playground/validator/blob/a947377040f8ebaee09f20d09a745ec369396793/baked_in.go#L2707-L2719 As these methods are private to the validator package so I can't reference them.

Code sample, to showcase or reproduce:

package main

import (
    "github.com/go-playground/validator/v10"
)

type Example struct {
    Email string `validate:"lcase_email|empty_string"`
}

func main() {
    validate := validator.New()
    validate.RegisterAlias("lcase_email", "email,lowercase")
    validate.RegisterAlias("empty_string", "eq=")

    ex := &Example{
        Email: "badger.smith@gmail.com",
    }

    err := validate.Struct(ex)
    if err != nil {
        println(err.Error())
    }
}