Scan from character number FROM by COUNT lists.
Scan forward if COUNT is positive, backward if COUNT is negative.
Return the character number of the position thus found.
A "list", in this context, refers to a balanced parenthetical
grouping, as determined by the syntax table.
If DEPTH is nonzero, treat that as the nesting depth of the starting
point (i.e. the starting point is DEPTH parentheses deep). This
function scans over parentheses until the depth goes to zero COUNT
times. Hence, positive DEPTH moves out that number of levels of
parentheses, while negative DEPTH moves to a deeper level.
Comments are ignored if `parse-sexp-ignore-comments' is non-nil.
If we reach the beginning or end of the accessible part of the buffer
before we have scanned over COUNT lists, return nil if the depth at
that point is zero, and signal a error if the depth is nonzero. (fn FROM COUNT DEPTH)