/usr/lib/swipl/library/ext/pldoc/pldoc/doc_htmlsrc.pl
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 source_to_html(+In:filename, +Out, :Options) is det
Colourise Prolog source as HTML. The idea is to first create a sequence of fragments and then to apply these to the code. Options are:
format_comments(+Boolean)
If true (default), use PlDoc formatting for structured comments.

Other options are passed to the following predicates:

Arguments:
In- A filename. Can also be an abstract name, which is subject to library(prolog_source) abstract file handling. See prolog_open_source/2. Note that this cannot be a stream as we need to read the file three times: (1) xref, (2) assign colours and (3) generate HTML.
Out- Term stream(Stream) or filename specification