0x prefix should not be stripped outside base 16.
versions.txt v5.71:
36.Fixed bug in $base(), can handle larger values. It now also strips out 0x number prefix, eg. from 0x0809.
I agree this is nice to recognize the 0x prefix for base 16, but should it actually be recognized in any other 'from' base besides 16? Currently, the only one where the 0x prefix is not stripped is base36. At the very least, it should be fixed to also not-strip the 0x prefix in bases 34-35 where X is a valid character.
//var %i 2 , %a , %value F | while (%i isnum 2-36) { var %a %a $+(base,%i,=,$base(0x $+ %value,%i,10),vs,$base(%value,%i,10)) | inc %i } | echo -a %a
Also would be nice if 0x prefix were mentioned in /help.