I see uuids on tabexpansion

Hi, when I just tabexpand in the console wihout a preceeding input or with e.g. ‘a’ I sometimes get a list of uuids or only 1 or none.

a                                         apply_defines
abb03033bb7346863d5d44beb1a791d181c9004b  apply_macros % <<< uuid
abi                                       apply_macros_sentinel
abi_version                               app_name
abnormal_thread_completion                app_preferences
abolish                                   apropos
abolish_all_tables                        arch
abolish_foreign                           arch_compatible_with
abolish_module_tables                     archive
abolish_monotonic_tables                  archive_close

The same happens when I use ‘$atom_completions’ :

(ins)?- '$atom_completions'( 'a', L).
L = [a, abb03033bb7346863d5d44beb1a791d181c9004b, abi, abi_version, abnormal_thread_completion, abolish, abolish_all_tables, abolish_foreign, abolish_module_tables|...].

Where are these uuids from? What does they mean?

And how can I get a complete list from ‘$atom_completions’ It seems to be incomplete when I call '$atom_completions'('', L).

I’m on swipl 9.2.2 .

Regards, Frank Schwidom