Call as $(runMarkers $path => “name of marker to run”) to run only named markers in the file at $path
Call as $(runMarkers $path) to run all markers in the file at $path
If $path is empty, it will try to point to the current file (there are limitations here until some RFCs land)
Named markers are embedded as $(marker “$name” => …)
Unnamed markers are embedded as $(marker => …)
Markers evaluate to nothing when run normally; the code in the … is run and the environment is captured when run via runMarkers
This gives you a way to (for example) set variables or define new handlers in one part of your source file, and use them in other invocations of do_with_in within the same source file