Rewrite validation groups explanation.

[dsuurlant]

Q	A
Doc fix?	yes
New docs?	no
Applies to	all (or 2.1+)
Fixed tickets	#2750

[bamarni]

I'm also confused about this section, why not removing User instead of Defaut though? From what I understand the class name is just another way to reference the Default group when using group sequences, as stated a few lines below :

Group sequences cannot contain the group Default, as this would create a loop. Instead, use the group {ClassName} (e.g. User) instead.

[dsuurlant]

I removed Default because it is not actually used as a group reference in the code. It exists on a logical level, but when you want to refer to it in Group Sequence, you use the entity's class name. Thus, listing 'Default' as one of the validation groups would be the most confusing.

[weaverryan]

Hi guys!

I think this is a nice clarification - @DanielleSuurlant I think mentioning just the 2 groups as you've done here is the best idea.

Thanks!