A row-level expression is a mathematical expression involving a single record (row) in the data. They are used to calculate derived fields but can also be used in custom metrics and admin-defined functions.
Row-level expressions are created using attributes and metrics from the data and row-level functions.
Be careful not to create row-level expressions using fields in a data source that have had their field data type changed. Doing so may generate errors for the row-level expression. Instead, use the original field (with its original field type) to create a derived field of the field type you need and then use the new derived field in your row-level expressions.