Function: sort-subr

General text sorting routine to divide buffer into records and sort them.

We divide the accessible portion of the buffer into disjoint pieces
called sort records. A portion of each sort record (perhaps all of
it) is designated as the sort key. The records are rearranged in the
buffer in order by their sort keys. The records may or may not be
contiguous.

Usually the records are rearranged in order of ascending sort key.
If REVERSE is non-nil, they are rearranged in order of descending sort key.
The variable `sort-fold-case' determines whether alphabetic case affects
the sort order.

The next four arguments are functions to be called to move point
across a sort record. They will be called many times from within sort-subr.

NEXTRECFUN is called with point at the end of the previous record.
It moves point to the start of the next record.
It should move point to the end of the buffer if there are no more records.
The first record is assumed to start at the position of point when sort-subr
is called.

ENDRECFUN is called with point within the record.
It should move point to the end of the record.

STARTKEYFUN moves from the start of the record to the start of the key.
It may return either a non-nil value to be used as the key, or
else the key is the substring between the values of point after
STARTKEYFUN and ENDKEYFUN are called. If STARTKEYFUN is nil, the key
starts at the beginning of the record.

ENDKEYFUN moves from the start of the sort key to the end of the sort key.
ENDKEYFUN may be nil if STARTKEYFUN returns a value or if it would be the
same as ENDRECFUN.

PREDICATE, if non-nil, is the predicate function for comparing
keys; it is called with two arguments, the keys to compare, and
should return non-nil if the first key should sort before the
second key. If PREDICATE is nil, comparison is done with `<' if
the keys are numbers, with `compare-buffer-substrings' if the
keys are cons cells (the car and cdr of each cons cell are taken as start and end positions), and with `string<' otherwise. (fn REVERSE NEXTRECFUN ENDRECFUN &optional STARTKEYFUN ENDKEYFUN PREDICATE)