type_sum controls how objects are shown when inside tibble
columns.
# S3 method for model_spec
type_sum(x)# S3 method for model_fit
type_sum(x)
A model_spec or model_fit object to summarise.
A character value.
For model_spec objects, the summary is "spec[?]"
or "spec[+]". The former indicates that either the model
mode has not been declared or that the specification has
varying() parameters. Otherwise, the latter is shown.
For fitted models, either "fit[x]" or "fit[+]" are used
where the "x" implies that the model fit failed in some way.