Type of metadata to write. Standard types include "flags", "sources", "properties", "metrics", and "evaluation". You can also specify a custom type (see Custom Types section below).

Metadata to write:

• "flags" — Named list of training flags

• "source" — Directory to copy source files from

• "properties" — Named list of arbitrary properties. Note that properties will be stored as strings.

• "metrics" — Data frame with training run metrics (see Metrics Data Frame below).

• "evaluation" — Named list of evaluation metrics.

• "error" — Named list with 'message' and 'traceback'

• "<custom>" – Function used to write the data (see Custom Types section below).