`for`. The `${}` form is a Javascript function, which can include
control blocks, and must end in a `return` statement.
-Dxpressions can both appear in `valueFrom` fields as well as some
+Expressions can both appear in `valueFrom` fields as well as some
other fields, or in an `ExpressionTool` which, like `Workflow` or
`CommandLineTool` has explicitly defined `inputs` and `outputs`
sections.