Get value from other fields

[psaikali]

I'm about to follow this template to create a new custom field. I'm not sure if the current codebase will allow me to access other CF fields values (from current post) from my new custom field though?

Here is my usage: I have a "Book" post type, and a "Note" post type.
A Note belongs to a specific Book, at a specific position in the Book content.
On the Note post type, I have a CF metabox to select the Book relationship.

Once a Book relationship has been made via a CF field, my new custom field will intercept this relationship field value and load the selected Book content. Then, my new custom field will let the user indicate the exact position for the Note.

So can I access a previous CF field value within another (custom) CF field?

Thanks for your help!