请解释以下代码：

Question

这是我在Django应用程序中的forms.py。但是我还不了解save（）函数，尤其是commit关键字。我从博客中获取了此代码。在这里，编写者正在制作用户注册表格。

from django import forms
from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth.models import User
from . models import Document

class NewUserForm(UserCreationForm):
    email = forms.EmailField(required=True)

    class Meta:
        model = User
        fields = ("username", "email", "password1", "password2")

    def save(self, commit = True):
        user = super(NewUserForm, self).save(commit = False)    
        user.email = self.cleaned_data["email"]
        if commit:
            user.save()
        return user    

请说明整个保存功能。