CapCruncher-style metadata
This example shows a custom metadata extractor for filenames shaped like:
sample.method.viewpoint.bigWig
The extractor returns fields such as samplename, method, and viewpoint. The builder then uses those fields as composite-track dimensions and puts derived track categories into supertracks.
This is useful when a project has a stable naming convention that the built-in extractors do not cover. Treat the regular expression as part of the project configuration: test it against a few representative paths before processing a whole result directory.
The example creates placeholder files to demonstrate the metadata logic. It prepares a HubBuilder and calls build() but does not call stage_hub(), so add that call when adapting the pattern to real data.