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Predicate xref_open_source/2
 prolog:xref_open_source(+SourceID, -Stream)[multifile, library(prolog_source)]
Hook to open an xref SourceID. This is used for cross-referencing non-files, such as XPCE buffers, files from archives, git repositories, etc. When successful, the corresponding prolog:xref_close_source/2 hook is called for closing the source.
 prolog:xref_open_source(+Id, -Stream) is semidet[multifile, 'pack_analyzer.pl']
If Id refers to a known Prolog pack, open the pack entry. A pack-file identifier is the path-name of the archive or pack directory, followed by the entry in the pack.
 prolog:xref_open_source(+Source, -Stream)[multifile, library(pce_prolog_xref)]
Open the PceEmacs as a Prolog stream.