--editable suppresses binary caching and source re-extraction for packages listed on the command line (similar to --head).
This fundamentally changes the port maintenance loop, so several example documents were updated. To avoid users having substantial changes suddenly destroyed by forgetting to pass --editable, "clean" sources have different extract locations.
The undocumented command `build` implies `--editable`.
Co-authored-by: Robert Schumacher <roschuma@microsoft.com>
