A quick and dirty definition of User Story:

"As a <role>, I want <goal/desire> so that <benefit>" 

In this commonly accepted definition there is little space for defining business rules, constraints or user input.

Trivial example just to illustrate:

As a <librarian>, I want to <register new books> so that <students 

can find their availability online>

In this silly example, where would one define the fields needed when registering a book? Should it be written anywhere? Or should the required business rules be passed as word of mouth by the Product Owner?

A quick and dirty definition of User Story:

"As a <role>, I want <goal/desire> so that <benefit>" 

In this commonly accepted definition there is little space for defining business rules, constraints or user input.

Trivial example just to illustrate:

"As a <librarian>, I want to <register new books> so that <students can find their availability online>" 

In this silly example, where would one define the fields needed when registering a book? Should it be written anywhere? Or should the required business rules be passed as word of mouth by the Product Owner?