Validate on specified field and display specific error message

Questions
3

Hm,

Then my code was right, is this feature available in 7.2.3?
Tried without the ToLower() but it always displays the message on top.

validationResult.AddError(“Id”.ToLower(), “already exists!”);
validationResult.AddError(“Id”, “already exists!”);

Tried also using “_name” but that also just appends the message to top and not on the actual field.

Update:
To be clear here, i’m using ValidationRuleBase<Page>
And validating page in Websites BO.