Derived fields join the column inspector
Expression dimensions, expression measures, the count of records and expression keys are now created and edited from the table page itself. The Keys, Dimensions and Measures tabs are gone: one column list, one inspector.
Add derived field
Above the column list, Add derived field offers four kinds: Expression dimension, Expression measure, Count of records and Expression key. The expression kinds open the formula editor in the inspector — the editor's title is the field's name — and the field lands under Derived, selected, as soon as you save. Count of records is added in one click.
Edit them where they live
Selecting a derived row opens the inspector on that one field: its formula with an Edit button, and everything else the field carries — kind, grains and geography for a dimension; aggregation, time axis, semi-additive window and filters for a measure; type, target and reverse join for a key. A derived measure's Source switches between the count of records and an expression. Custom dimensions can be renamed here too.
Metrics keep their tab beside Columns until they get a page of their own.