The documentation (https://docs.qgis.org/3.4/en/docs/user_manual/working_with_vector/expression.html#id31) says:
To use these functions in an expression, they should be preceded by @ character (e.g, @row_number).
map_scale is one of these variables. But if you see the example
map_get( item_variables('Map 0'), 'map_scale')it is used without an
Why is it in this case used without an