Name of the lambda argument treated as an implicit inner pipe

Most macros are expanded before the pipe is processed. This is the list of exceptions.

Result of the previous pipeline step

Replacements to perform within pipes, before other transformations.

Wrap first argument of a kwexpr into a StopWalk so that it's not processed in the walk afterwards.

Replace function arg placeholders (like _) with corresponding symbols from args. Processes a single level of @p nesting.

Replace symbols in expr according to syms_replacemap.