Description of `program-sources' and accessors

[Diogo F. S. Ramos]

Is there a place which describes the meaning of each of element of
`program-sources' accessors?

For example:

  (source:addr (program-sources every)) => (0 "srfi/srfi-1.scm" 810 . 0)

What does each element of the improper list mean?

Also for `source:file', `source:line' and `source:column'.  The first
two are also improper lists, but the last is a list of improper lists.