The partial source files for the runtime library interpreter programs are provided as source archive files. The source files mainly include Prolog texts and Java classes. But they might also include other types of artefacts.
The support files archive contains the following sources:
05_run # Runtime Library
+--- 02_reference # Language Reference
+--- 05_frequent # Frequent Predicates
The source archive files are located in the files package.zip in the above directories.
The sources are mainly there to give a more detailed documentation of the inner working of the interpreter. But the sources can also be used to create derivative work, except for special predicates, which currently come without source.