New to expressions and formulas? Try Expressions: The Essentials.
New to column constraints? Try Column Constraints.
You can also learn more about other types of expressions.
Expressions in this article align with the Yes/No Expressions in Expression Builder in the app editor.
When an input column is "editable", it can be modified by the user. The Editable_If column constraint is useful to lock down a column (to prevent user edits) depending on the value already in the column or on the values of other columns.
An Editable_If constraint is a condition expression that indicates if a specific column is "editable" in an input form. For instance, ISBLANK([_THIS]) allows edits only if the current value is blank, but once there is a value, the field cannot be edited. Another common use case is to give certain users the ability to edit a field, but make it read-only for others (e.g. USEREMAIL() = "firstname.lastname@example.org").