Not all data types can be coerced to numeric

[elinw]

When skim encounters an unknown data type it attempts to coerce to numeric and do a set of default functions for numeric.
However, some data types, such as lists, cannot be coerced to numeric. In that case the following error is returned:

Error: (list) object cannot be coerced to type 'double'

Perhaps it would be good to use character as a fallback rather than numeric.