The default formatting, which is recommended in Held and Ott (2018), is as follows :
For very small Bayes factors BF < 1/1000, "< 1/1000" is returned.
Bayes factors BF with 1/1000 <= BF <=1/10 are formatted as 1/x, where x is an integer
and Bayes factors BF with 1/10 < BF < 1 as
1/x, where x is rounded to one decimal place.
Accordingly, Bayes factors 1 <= BF < 10 are rounded to one decimal place,
Bayes factors 10 <= BF <= 1000 are rounded to the next integer
and for larger Bayes factors, "> 1000" is returned.
If digits
is specified,
the Bayes factor (if it is >= 1) or its inverse (if the Bayes factor is <1)
is rounded to the number of decimal places specified
and returned as a ratio if the Bayes factor is <1.