According to my copy of BaseX 10.7,

string:levenshtein('oil field', 'oilfield')

and 

string:levenshtein('oil field', 'coalfield') 

both return the same value, 0.7777777777777778.

My understanding is that the Levenshtein-Damerau distance between 'oil field' and 'oilfield' is 1 and between 'oil field' and 'coalfield' is 3, so following the formula from https://docs.basex.org/wiki/String_Module#string:levenshtein

1.0 – distance / max(length of strings)

should give 0.888... and 0.666... respectively.

Am I off-base here or is there something awry with string:levenshtein?

Cheers,

Jack