Debugger output: where to look for its explanation?

[Marcin Borkowski <mbork@wmi.amu.edu.pl>]

Hi all,

so I got this as a *Backtrace*:

--8<---------------cut here---------------start------------->8---
Debugger entered--Lisp error: (scan-error "Containing expression ends prematurely" 2959 2959)
  scan-sexps(2980 -3)
  forward-sexp(-3)
  backward-sexp(3)
  (let ((beg-string (nth 8 (syntax-ppss))) (current-line (line-number-at-pos))) (goto-char beg-string) (backward-sexp 3) (if (and (member (symbol-at-point) symbols-with-docstrings) (looking-back "^(")) (progn (goto-char beg-string) (forward-sexp) (or (> (line-number-at-pos) current-line) (is-current-line-comment-only-p)))))
  (if (and (eq major-mode (quote emacs-lisp-mode)) (nth 3 (syntax-ppss))) (let ((beg-string (nth 8 (syntax-ppss))) (current-line (line-number-at-pos))) (goto-char beg-string) (backward-sexp 3) (if (and (member (symbol-at-point) symbols-with-docstrings) (looking-back "^(")) (progn (goto-char beg-string) (forward-sexp) (or (> (line-number-at-pos) current-line) (is-current-line-comment-only-p))))))
  (save-excursion (skip-syntax-forward "\"-") (if (and (eq major-mode (quote emacs-lisp-mode)) (nth 3 (syntax-ppss))) (let ((beg-string (nth 8 (syntax-ppss))) (current-line (line-number-at-pos))) (goto-char beg-string) (backward-sexp 3) (if (and (member (symbol-at-point) symbols-with-docstrings) (looking-back "^(")) (progn (goto-char beg-string) (forward-sexp) (or (> (line-number-at-pos) current-line) (is-current-line-comment-only-p)))))))
  is-current-line-docstring-p()
  eval((is-current-line-docstring-p) nil)
  eval-expression((is-current-line-docstring-p) nil)
  funcall-interactively(eval-expression (is-current-line-docstring-p) nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)
--8<---------------cut here---------------end--------------->8---

etc.

I grepped both the Emacs manual and the Elisp reference for "Lisp
error", but couldn't find specific info.

What do the 2959 2959 mean?  (I assume they are some positions in the
buffer; I found out that they correspond to the beginning of the line
where the error manifested itself - but what are they exactly?)

I'm rather confident that the numbers in parens after function names are
their arguments.

OTOH, some of these lines contain forms and not functions.  Why?  Why is
my function ("is-current-line-docstring-p") "split" into forms
(save-excursion, if and let) and other functions are not?

Some of the function names are clickable and some are not.  Why?  (I
would assume that the Elisp ones are clickable and the C ones are not.
Correct?)

TIA,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University