You're seeing just the function track_parser, go back to Ergo.Context module for more information.
Link to this function

track_parser(ctx, ref, data)

Updates the Context to track that the parser referred to by ref has been called for the index index.


iex> alias Ergo.Context
iex> import Ergo.Terminals
iex> context ="Hello World")
iex> parser = literal("Hello")
iex> context2 = Context.track_parser(context, parser.ref, :foo)
iex> assert Map.has_key?(context2.tracks, {0, parser.ref})