The base pipe has an underscore as a placeholder. From the docs:

Usage:

     lhs |> rhs

Arguments:

     lhs: expression producing a value.

     rhs: a call expression. 

Details: [...]

     It is also possible to use a named argument with the placeholder
     ‘_’ in the ‘rhs’ call to specify where the ‘lhs’ is to be
     inserted.  The placeholder can only appear once on the ‘rhs’.