Hello,
In my previous query "Required condition in the fields - filter to enable save draft", you have mentioned as "validation works by JavaScript code or browser filter".
As I noticed from the documentation Validation,
There are 2 ways of doing validation: via input attributes (mostly for basic validation) and via jQuery validation plugin (for more advanced validation).
Validation via input attributes is customizable?
Is there any custom code to use server-side validation to save the post and restrict to publish?