Scadnano supports the notion of a label attached to a strand, domain, loopout, or extension.

Currently, the type of label is an arbitrary JSON-serializable object. However, this makes type checking awkward, and since such objects can be mutable, the web interface (which relies on immutable state date) might have unforeseen problems due to this.

It would be simpler to simply say the type of label is a string. If a user wants more structured data, they can do the JSON serialization and deserialization themselves. Note that this will be a breaking change.

See UC-Davis-molecular-computing/scadnano#878