/usr/share/source-highlight/sml.lang is in libsource-highlight-common 3.1.7-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | include "caml.lang"
redef keyword = "abstraction|abstype|and|andalso|as|before|case|datatype|do|else|end|eqtype|exception|fn|fun|functor|handle|if|in|include|infix|infixr|let|local|nonfix|o|of|op|open|orelse|overload|raise|rec|sharing|sig|signature|struct|structure|then|type|val|where|while|with|withtype"
redef type = "int|byte|boolean|char|long|float|double|short|void"
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